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Lawyers, other representatives, expert(s), tribunal’s secretary

    Judgment

    1.
    By a letter dated 2 July 1993, filed in the Registry of the Court on the same day, the Ambassador of the Republic of Hungary (hereinafter called "Hungary") to the Netherlands and the Chargé d’affaires ad interim of the Slovak Republic (hereinafter called "Slovakia") to the Netherlands jointly notified to the Court a Special Agreement in English that had been signed at Brussels on 7 April 1993 and had entered into force on 28 June 1993, on the date of the exchange of instruments of ratification.
    2.
    The text of the Special Agreement reads as follows:

    "The Republic of Hungary and the Slovak Republic,

    Considering that differences have arisen between the Czech and Slovak Federal Republic and the Republic of Hungary regarding the implementation and the termination of the Treaty on the Construction and Operation of the Gabčikovo-Nagymaros Barrage System signed in Budapest on 16 September 1977 and related instruments (hereinafter referred to as ‘the Treaty’), and on the construction and operation of the ‘provisional solution’;

    Bearing in mind that the Slovak Republic is one of the two successor States of the Czech and Slovak Federal Republic and the sole successor State in respect of rights and obligations relating to the Gabčikovo-Nagymaros Project;

    Recognizing that the Parties concerned have been unable to settle these differences by negotiations;

    Having in mind that both the Czechoslovak and Hungarian delegations expressed their commitment to submit the differences connected with the Gabčikovo-Nagymaros Project in all its aspects to binding international arbitration or to the International Court of Justice;

    Desiring that these differences should be settled by the International Court of Justice;

    Recalling their commitment to apply, pending the Judgment of the International Court of Justice, such a temporary water management régime of the Danube as shall be agreed between the Parties;

    Desiring further to define the issues to be submitted to the International Court of Justice,

    Have agreed as follows:

    Article I

    The Parties submit the questions contained in Article 2 to the International Court of Justice pursuant to Article 40, paragraph 1, of the Statute of the Court.

    Article 2

    (1) The Court is requested to decide on the basis of the Treaty and rules and principles of general international law, as well as such other treaties as the Court may find applicable,

    (a) whether the Republic of Hungary was entitled to suspend and subsequently abandon, in 1989, the works on the Nagymaros Project and on the part of the Gabčikovo Project for which the Treaty attributed responsibility to the Republic of Hungary;

    (b) whether the Czech and Slovak Federal Republic was entitled to proceed, in November 1991, to the ‘provisional solution’ and to put into operation from October 1992 this system, described in the Report of the Working Group of Independent Experts of the Commission of the European Communities, the Republic of Hungary and the Czech and Slovak Federal Republic dated 23 November 1992 (damming up of the Danube at river kilometre 1851.7 on Czechoslovak territory and resulting consequences on water and navigation course);

    (c) what are the legal effects of the notification, on 19 May 1992, of the termination of the Treaty by the Republic of Hungary.

    (2) The Court is also requested to determine the legal consequences, including the rights and obligations for the Parties, arising from its Judgment on the questions in paragraph 1 of this Article.

    Article 3

    (1) All questions of procedure and evidence shall be regulated in accordance with the provisions of the Statute and the Rules of Court.

    (2) However, the Parties request the Court to order that the written proceedings should consist of :

    (a) a Memorial presented by each of the Parties not later than ten months after the date of notification of this Special Agreement to the Registrar of the International Court of Justice;

    (b) a Counter-Memorial presented by each of the Parties not later than seven months after the date on which each has received the certified copy of the Memorial of the other Party;

    (c) a Reply presented by each of the Parties within such time-limits as the Court may order.

    (d) The Court may request additional written pleadings by the Parties if it so determines.

    (3) The above-mentioned parts of the written proceedings and their annexes presented to the Registrar will not be transmitted to the other Party until the Registrar has received the corresponding part of the proceedings from the said Party.

    Article 4

    (1) The Parties agree that, pending the final Judgment of the Court, they will establish and implement a temporary water management régime for the Danube.

    (2) They further agree that, in the period before such a régime is established or implemented, if either Party believes its rights are endangered by the conduct of the other, it may request immediate consultation and reference, if necessary, to experts, including the Commission of the European Communities, with a view to protecting those rights; and that protection shall not be sought through a request to the Court under Article 41 of the Statute.

    (3) This commitment is accepted by both Parties as fundamental to the conclusion and continuing validity of the Special Agreement.

    Article 5

    (1) The Parties shall accept the Judgment of the Court as final and binding upon them and shall execute it in its entirety and in good faith.

    (2) Immediately after the transmission of the Judgment the Parties shall enter into negotiations on the modalities for its execution.

    (3) If they are unable to reach agreement within six months, either Party may request the Court to render an additional Judgment to determine the modalities for executing its Judgment.

    Article 6

    (1) The present Special Agreement shall be subject to ratification.

    (2) The instruments of ratification shall be exchanged as soon as possible in Brussels.

    (3) The present Special Agreement shall enter into force on the date of exchange of instruments of ratification. Thereafter it will be notified jointly to the Registrar of the Court.

    In witness whereof the undersigned being duly authorized thereto, have signed the present Special Agreement and have affixed thereto their seals."

    3.
    Pursuant to Article 40, paragraph 3, of the Statute and Article 42 of the Rules of Court, copies of the notification and of the Special Agreement were transmitted by the Registrar to the Secretary-General of the United Nations, Members of the United Nations and other States entitled to appear before the Court.
    4.
    Since the Court included upon the Bench no judge of Slovak nationality, Slovakia exercised its right under Article 31, paragraph 2, of the Statute to choose a judge ad hoc to sit in the case: it chose Mr. Krzysztof Jan Skubiszewski.
    5.
    By an Order dated 14 July 1993, the Court fixed 2 May 1994 as the timelimit for the filing by each of the Parties of a Memorial and 5 December 1994 for the filing by each of the Parties of a Counter-Memorial, having regard to the provisions of Article 3, paragraph 2 (a) and (b), of the Special Agreement. Those pleadings were duly filed within the prescribed time-limits.
    6.
    By an Order dated 20 December 1994, the President of the Court, having heard the Agents of the Parties, fixed 20 June 1995 as the time-limit for the filing of the Replies, having regard to the provisions of Article 3, paragraph 2 (c), of the Special Agreement. The Replies were duly filed within the time-limit thus prescribed and, as the Court had not asked for the submission of additional pleadings, the case was then ready for hearing.
    7.
    By letters dated 27 January 1997, the Agent of Slovakia, referring to the provisions of Article 56, paragraph 1, of the Rules of Court, expressed his Government’s wish to produce two new documents; by a letter dated 10 February 1997, the Agent of Hungary declared that his Government objected to their production. On 26 February 1997, after having duly ascertained the views of the two Parties, the Court decided, in accordance with Article 56, paragraph 2, of the Rules of Court, to authorize the production of those documents under certain conditions of which the Parties were advised. Within the time-limit fixed by the Court to that end, Hungary submitted comments on one of those documents under paragraph 3 of that same Article. The Court authorized Slovakia to comment in turn upon those observations, as it had expressed a wish to do so; its comments were received within the time-limit prescribed for that purpose.
    8.
    Moreover, each of the Parties asked to be allowed to show a video cassette in the course of the oral proceedings. The Court agreed to those requests, provided that the cassettes in question were exchanged in advance between the Parties, through the intermediary of the Registry. That exchange was effected accordingly.
    9.
    In accordance with Article 53, paragraph 2, of the Rules of Court, the Court decided, after having ascertained the views of the Parties, that copies of the pleadings and documents annexed would be made available to the public as from the opening of the oral proceedings.
    10.
    By a letter dated 16 June 1995, the Agent of Slovakia invited the Court to visit the locality to which the case relates and there to exercise its functions with regard to the obtaining of evidence, in accordance with Article 66 of the Rules of Court. For his part, the Agent of Hungary indicated, by a letter dated 28 June 1995, that, if the Court should decide that a visit of that kind would be useful, his Government would be pleased to co-operate in organizing it. By a letter dated 14 November 1995, the Agents of the Parties jointly notified to the Court the text of a Protocol of Agreement, concluded in Budapest and New York the same day, with a view to proposing to the Court the arrangements that might be made for such a visit in situ; and, by a letter dated 3 February 1997, they jointly notified to it the text of Agreed Minutes drawn up in Budapest and New York the same day, which supplemented the Protocol of Agreement of 14 November 1995. By an Order dated 5 February 1997, the Court decided to accept the invitation to exercise its functions with regard to the obtaining of evidence at a place to which the case relates and, to that end, to adopt the arrangements proposed by the Parties. The Court visited the area from 1 to 4 April 1997; it visited a number of locations along the Danube and took note of the technical explanations given by the representatives who had been designated for the purpose by the Parties.
    11.
    The Court held a first round of ten public hearings from 3 to 7 March and from 24 to 27 March 1997, and a second round of four public hearings on 10, 11, 14 and 15 April 1997, after having made the visit in situ referred to in the previous paragraph. During those hearings, the Court heard the oral arguments and replies of :

    For Hungary:

    H.E. Mr. Szénási,

    Professor Valki,

    Professor Kiss,

    Professor Vida,

    Professor Carbiener,

    Professor Crawford,

    Professor Nagy,

    Dr. Kern,

    Professor Wheater,

    Ms Gorove,

    Professor Dupuy,

    Professor Sands.

    For Slovakia:

    H.E. Dr. Tomka,

    Dr. Mikulka,

    Mr. Wordsworth,

    Professor McCaffrey,

    Professor Mucha,

    Professor Pellet,

    Mr. Refsgaard,

    Sir Arthur Watts.

    12.
    The Parties replied orally and in writing to various questions put by Members of the Court. Referring to the provisions of Article 72 of the Rules of Court, each of the Parties submitted to the Court its comments upon the replies given by the other Party to some of those questions.
    13.
    In the course of the written proceedings, the following submissions were presented by the Parties :

    On behalf of Hungary,

    in the Memorial, the Counter-Memorial and the Reply (mutatis mutandis identical texts):

    "On the basis of the evidence and legal argument presented in the Memorial, Counter-Memorial and this Reply, the Republic of Hungary

    Requests the Court to adjudge and declare

    First, that the Republic of Hungary was entitled to suspend and subsequently abandon the works on the Nagymaros Project and on the part of the Gabčikovo Project for which the Treaty attributed responsibility to the Republic of Hungary;

    Second, that the Czech and Slovak Federal Republic was not entitled to proceed to the ‘provisional solution’ (damming up of the Danube at river kilometre 1851.7 on Czechoslovak territory and resulting consequences on water and navigation course);

    Third, that by its Declaration of 19 May 1992, Hungary validly terminated the Treaty on the Construction and Operation of the Gabčikovo-Nagymaros Barrage System of 16 September 1977:

    Requests the Court to adjudge and declare further

    that the legal consequences of these findings and of the evidence and the arguments presented to the Court are as follows:

    (1) that the Treaty of 16 September 1977 has never been in force between the Republic of Hungary and the Slovak Republic;

    (2) that the Slovak Republic bears responsibility to the Republic of Hungary for maintaining in operation the ‘provisional solution’ referred to above ;

    (3) that the Slovak Republic is internationally responsible for the damage and loss suffered by the Republic of Hungary and by its nationals as a result of the ‘provisional solution’;

    (4) that the Slovak Republic is under an obligation to make reparation in respect of such damage and loss, the amount of such reparation, if it cannot be agreed by the Parties within six months of the date of the Judgment of the Court, to be determined by the Court;

    (5) that the Slovak Republic is under the following obligations:

    (a) to return the waters of the Danube to their course along the international frontier between the Republic of Hungary and the Slovak Republic, that is to say the main navigable channel as defined by applicable treaties;

    (b) to restore the Danube to the situation it was in prior to the putting into effect of the provisional solution; and

    (c) to provide appropriate guarantees against the repetition of the damage and loss suffered by the Republic of Hungary and by its nationals."

    On behalf of Slovakia,

    in the Memorial, the Counter-Memorial and the Reply (mutatis mutandis identical texts):

    "On the basis of the evidence and legal arguments presented in the Slovak Memorial, Counter-Memorial and in this Reply, and reserving the right to supplement or amend its claims in the light of further written pleadings, the Slovak Republic

    Requests the Court to adjudge and declare:

    1. That the Treaty between Czechoslovakia and Hungary of 16 September 1977 concerning the construction and operation of the Gabčikovo/ Nagymaros System of Locks, and related instruments, and to which the Slovak Republic is the acknowledged successor, is a treaty in force and has been so from the date of its conclusion ; and that the notification of termination by the Republic of Hungary on 19 May 1992 was without legal effect.

    2. That the Republic of Hungary was not entitled to suspend and subsequently abandon the works on the Nagymaros Project and on that part of the Gabčikovo Project for which the 1977 Treaty attributed responsibility to the Republic of Hungary.

    3. That the act of proceeding with and putting into operation Variant C, the ‘provisional solution’, was lawful.

    4. That the Republic of Hungary must therefore cease forthwith all conduct which impedes the full and bona fide implementation of the 1977 Treaty and must take all necessary steps to fulfil its own obligations under the Treaty without further delay in order to restore compliance with the Treaty.

    5. That, in consequence of its breaches of the 1977 Treaty, the Republic of Hungary is liable to pay, and the Slovak Republic is entitled to receive, full compensation for the loss and damage caused to the Slovak Republic by those breaches, plus interest and loss of profits, in the amounts to be determined by the Court in a subsequent phase of the proceedings in this case."

    14.
    In the oral proceedings, the following submissions were presented by the Parties

    On behalf of Hungary,

    at the hearing of 11 April 1997 :

    The submissions read at the hearing were mutatis mutandis identical to those presented by Hungary during the written proceedings.

    On behalf of Slovakia,

    at the hearing of 15 April 1997:

    "On the basis of the evidence and legal arguments presented in its written and oral pleadings, the Slovak Republic,

    Requests the Court to adjudge and declare :

    1. That the Treaty, as defined in the first paragraph of the Preamble to the Compromis between the Parties, dated 7 April 1993, concerning the construction and operation of the Gabčikovo/Nagymaros System of Locks and related instruments, concluded between Hungary and Czechoslovakia and with regard to which the Slovak Republic is the successor State, has never ceased to be in force and so remains, and that the notification of 19 May 1992 of purported termination of the Treaty by the Republic of Hungary was without legal effect;

    2. That the Republic of Hungary was not entitled to suspend and subsequently abandon the works on the Nagymaros Project and on that part of the Gabčikovo Project for which the 1977 Treaty attributes responsibility to the Republic of Hungary;

    3. That the Czech and Slovak Federal Republic was entitled, in November 1991, to proceed with the ‘provisional solution’ and to put this system into operation from October 1992; and that the Slovak Republic was, and remains, entitled to continue the operation of this system ;

    4. That the Republic of Hungary shall therefore cease forthwith all conduct which impedes the bona fide implementation of the 1977 Treaty and shall take all necessary steps to fulfil its own obligations under the Treaty without further delay in order to restore compliance with the Treaty, subject to any amendments which may be agreed between the Parties ;

    5. That the Republic of Hungary shall give appropriate guarantees that it will not impede the performance of the Treaty, and the continued operation of the system;

    6. That, in consequence of its breaches of the 1977 Treaty, the Republic of Hungary shall, in addition to immediately resuming performance of its Treaty obligations, pay to the Slovak Republic full compensation for the loss and damage, including loss of profits, caused by those breaches together with interest thereon;

    7. That the Parties shall immediately begin negotiations with a view, in particular, to adopting a new timetable and appropriate measures for the implementation of the Treaty by both Parties, and to fixing the amount of compensation due by the Republic of Hungary to the Slovak Republic; and that, if the Parties are unable to reach an agreement within six months, either one of them may request the Court to render an additional Judgment to determine the modalities for executing its Judgment."

    15.
    The present case arose out of the signature, on 16 September 1977, by the Hungarian People’s Republic and the Czechoslovak People’s Republic, of a treaty "concerning the construction and operation of the Gabčikovo-Nagymaros System of Locks" (hereinafter called the "1977 Treaty"). The names of the two contracting States have varied over the years; hereinafter they will be referred to as Hungary and Czechoslovakia. The 1977 Treaty entered into force on 30 June 1978.

    It provides for the construction and operation of a System of Locks by the parties as a "joint investment". According to its Preamble, the barrage system was designed to attain

    "the broad utilization of the natural resources of the Bratislava-Budapest section of the Danube river for the development of water resources, energy, transport, agriculture and other sectors of the national economy of the Contracting Parties".

    The joint investment was thus essentially aimed at the production of hydroelectricity, the improvement of navigation on the relevant section of the Danube and the protection of the areas along the banks against flooding. At the same time, by the terms of the Treaty, the contracting parties undertook to ensure that the quality of water in the Danube was not impaired as a result of the Project, and that compliance with the obligations for the protection of nature arising in connection with the construction and operation of the System of Locks would be observed.

    16.
    The Danube is the second longest river in Europe, flowing along or across the borders of nine countries in its 2,860-kilometre course from the Black Forest eastwards to the Black Sea. For 142 kilometres, it forms the boundary between Slovakia and Hungary. The sector with which this case is concerned is a stretch of approximately 200 kilometres, between Bratislava in Slovakia and Budapest in Hungary. Below Bratislava, the river gradient decreases markedly, creating an alluvial plain of gravel and sand sediment. This plain is delimited to the north-east, in Slovak territory, by the Maly Danube and to the south-west, in Hungarian territory, by the Mosoni Danube. The boundary between the two States is constituted, in the major part of that region, by the main channel of the river. The area lying between the Maly Danube and that channel, in Slovak territory, constitutes the Zitny Ostrov; the area between the main channel and the Mosoni Danube, in Hungarian territory, constitutes the Szigetkoz. Cunovo and, further downstream, Gabčikovo, are situated in this sector of the river on Slovak territory, Cunovo on the right bank and Gabčikovo on the left. Further downstream, after the confluence of the various branches, the river enters Hungarian territory and the topography becomes hillier. Nagymaros lies in a narrow valley at a bend in the Danube just before it turns south, enclosing the large river island of Szentendre before reaching Budapest (see sketch-map No. 1, p. 19 below).
    17.
    The Danube has always played a vital part in the commercial and economic development of its riparian States, and has underlined and reinforced their interdependence, making international co-operation essential. Improvements to the navigation channel have enabled the Danube, now linked by canal to the Main and thence to the Rhine, to become an important navigational artery connecting the North Sea to the Black Sea. In the stretch of river to which the case relates, flood protection measures have been constructed over the centuries, farming and forestry practised, and, more recently, there has been an increase in population and industrial activity in the area. The cumulative effects on the river and on the environment of various human activities over the years have not all been favourable, particularly for the water régime.

    Only by international co-operation could action be taken to alleviate these problems. Water management projects along the Danube have frequently sought to combine navigational improvements and flood protection with the production of electricity through hydroelectric power plants. The potential of the Danube for the production of hydroelectric power has been extensively exploited by some riparian States. The history of attempts to harness the potential of the particular stretch of the river at issue in these proceedings extends over a 25-year period culminating in the signature of the 1977 Treaty.

    18.
    Article 1, paragraph 1, of the 1977 Treaty describes the principal works to be constructed in pursuance of the Project. It provided for the building of two series of locks, one at Gabčikovo (in Czechoslovak territory) and the other at Nagymaros (in Hungarian territory), to constitute "a single and indivisible operational system of works" (see sketch-map No. 2, p. 21 below). The Court will subsequently have occasion to revert in more detail to those works, which were to comprise, inter alia, a reservoir upstream of Dunakiliti, in Hungarian and Czechoslovak territory; a dam at Dunakiliti, in Hungarian territory; a bypass canal, in Czechoslovak territory, on which was to be constructed the Gabčikovo System of Locks (together with a hydroelectric power plant with an installed capacity of 720 megawatts (MW)); the deepening of the bed of the Danube downstream of the place at which the bypass canal was to rejoin the old bed of the river; a reinforcement of flood-control works along the Danube upstream of Nagymaros; the Nagymaros System of Locks, in Hungarian territory (with a hydroelectric power plant of a capacity of 158 MW) ; and the deepening of the bed of the Danube downstream.

    Article 1, paragraph 4, of the Treaty further provided that the technical specifications concerning the system would be included in the "Joint Contractual Plan" which was to be drawn up in accordance with the Agreement signed by the two Governments for this purpose on 6 May 1976; Article 4, paragraph 1, for its part, specified that "the joint investment [would] be carried out in conformity with the joint contractual plan".

    According to Article 3, paragraph 1 :

    "Operations connected with the realization of the joint investment and with the performance of tasks relating to the operation of the System of Locks shall be directed and supervised by the Governments of the Contracting Parties through...(... ‘government delegates’)."

    Those delegates had, inter alia, "to ensure that construction of the System of Locks is... carried out in accordance with the approved joint contractual plan and the project work schedule". When the works were brought into operation, they were moreover "To establish the operating and operational procedures of the System of Locks and ensure compliance therewith."

    Article 4, paragraph 4, stipulated that :

    "Operations relating to the joint investment [should] be organized by the Contracting Parties in such a way that the power generation plants [would] be put into service during the period 1986-1990."

    Article 5 provided that the cost of the joint investment would be borne by the contracting parties in equal measure. It specified the work to be carried out by each one of them. Article 8 further stipulated that the Dunakiliti dam, the bypass canal and the two series of locks at Gabčikovo and Nagymaros would be "jointly owned" by the contracting parties "in equal measure". Ownership of the other works was to be vested in the State on whose territory they were constructed.

    The parties were likewise to participate in equal measure in the use of the system put in place, and more particularly in the use of the base-load and peak-load power generated at,the hydroelectric power plants (Art. 9).

    According to Article 10, the works were to be managed by the State on whose territory they were located, "in accordance with the jointly-agreed operating and operational procedures", while Article 12 stipulated that the operation, maintenance (repair) and reconstruction costs of jointly owned works of the System of Locks were also to be borne jointly by the contracting parties in equal measure.

    According to Article 14,

    "The discharge specified in the water balance of the approved joint contractual plan shall be ensured in the bed of the Danube [between Dunakiliti and Sap] unless natural conditions or other circumstances temporarily require a greater or smaller discharge."

    Paragraph 3 of that Article was worded as follows :

    "In the event that the withdrawal of water in the Hungarian-Czechoslovak section of the Danube exceeds the quantities of water specified in the water balance of the approved joint contractual plan and the excess withdrawal results in a decrease in the output of electric power, the share of electric power of the Contracting Party benefiting from the excess withdrawal shall be correspondingly reduced."

    Article 15 specified that the contracting parties

    "shall ensure, by the means specified in the joint contractual plan, that the quality of the water in the Danube is not impaired as a result of the construction and operation of the System of Locks".

    Article 16 set forth the obligations of the contracting parties concerning the maintenance of the bed of the Danube.

    Article 18, paragraph 1, provided as follows:

    "The Contracting Parties, in conformity with the obligations previously assumed by them, and in particular with article 3 of the Convention concerning the regime of navigation on the Danube, signed at Belgrade on 18 August 1948, shall ensure uninterrupted and safe navigation on the international fairway both during the construction and during the operation of the System of Locks."

    It was stipulated in Article 19 that:

    "The Contracting Parties shall, through the means specified in the joint contractual plan, ensure compliance with the obligations for the protection of nature arising in connection with the construction and operation of the System of Locks."

    Article 20 provided for the contracting parties to take appropriate measures, within the framework of their national investments, for the protection of fishing interests in conformity with the Convention concerning Fishing in the Waters of the Danube, signed at Bucharest on 29 January 1958.

    According to Article 22, paragraph 1, of the Treaty, the contracting parties had, in connection with the construction and operation of the System of Locks, agreed on minor revision to the course of the State frontier between them as follows:

    "(d) In the Dunakiliti-Hrusov head-water area, the State frontier shall run from boundary point 161.V.O.á. to boundary stone No. 1.5. in a straight line in such a way that the territories affected, to the extent of about 10-10 hectares shall be offset between the two States."

    It was further provided, in paragraph 2, that the revision of the State frontier and the exchange of territories so provided for should be effected "by the Contracting Parties on the basis of a separate treaty". No such treaty was concluded.

    Finally a dispute settlement provision was contained in Article 27, worded as follows:

    "1. The settlement of disputes in matters relating to the realization and operation of the System of Locks shall be a function of the government delegates.

    2. If the government delegates are unable to reach agreement on the matters in dispute, they shall refer them to the Governments of the Contracting Parties for decision."

    19.
    The Joint Contractual Plan, referred to in the previous paragraph, set forth, on a large number of points, both the objectives of the system and the characteristics of the works. In its latest version it specified in paragraph 6.2 that the Gabčikovo bypass canal would have a discharge capacity of 4,000 cubic metres per second (m3/s). The power plant would include "Eight... turbines with 9.20 m diameter running wheels" and would "mainly operate in peak-load time and continuously during high water". This type of operation would give an energy production of 2,650 gigawatt/hours (GWh) per annum. The Plan further stipulated in paragraph 4.4.2:

    "The low waters are stored every day, which ensures the peakload time operation of the Gabčikovo hydropower plant... a minimum of 50 m3/s additional water is provided for the old bed [of the Danube] besides the water supply of the branch system."

    The Plan further specified that, in the event that the discharge into the bypass canal exceeded 4,000-4,500 m3/s, the excess amounts of water would be channelled into the old bed. Lastly, according to paragraph 7.7 of the Plan:

    "The common operational regulation stipulates that concerning the operation of the Dunakiliti barrage in the event of need during the growing season 200 m3/s discharge must be released into the old Danube bed, in addition to the occasional possibilities for rinsing the bed."

    The Joint Contractual Plan also contained "Preliminary Operating and Maintenance Rules", Article 23 of which specified that "The final operating rules [should] be approved within a year of the setting into operation of the system." (Joint Contractual Plan, Summary Documentation, Vol. O-l-A.)

    Nagymaros, with six turbines, was, according to paragraph 6.3 of the Plan, to be a "hydropower station... type of a basic power-station capable of operating in peak-load time for five hours at the discharge interval between 1,000-2,500 m3/s" per day. The intended annual produc. tion was to be 1,025 GWh (i.e., 38 per cent of the production of Gabčikovo, for an installed power only equal to 21 per cent of that of Gabčikovo).

    20.
    Thus, the Project was to have taken the form of an integrated joint project with the two contracting parties on an equal footing in respect of the financing, construction and operation of the works. Its single and indivisible nature was to have been realized through the Joint Contractual Plan which complemented the Treaty. In particular, Hungary would have had control of the sluices at Dunakiliti and the works at Nagymaros, whereas Czechoslovakia would have had control of the works at Gabčikovo.
    21.
    The schedule of work had for its part been fixed in an Agreement on mutual assistance signed by the two parties on 16 September 1977, at the same time as the Treaty itself. The Agreement moreover made some adjustments to the allocation of the works between the parties as laid down by the Treaty.

    Work on the Project started in 1978. On Hungary’s initiative, the two parties first agreed, by two Protocols signed on 10 October 1983 (one amending Article 4, paragraph 4, of the 1977 Treaty and the other the Agreement on mutual assistance), to slow the work down and to postpone putting into operation the power plants, and then, by a Protocol signed on 6 February 1989 (which amended the Agreement on mutual assistance), to accelerate the Project.

    22.
    As a result of intense criticism which the Project had generated in Hungary, the Hungarian Government decided on 13 May 1989 to suspend the works at Nagymaros pending the completion of various studies which the competent authorities were to finish before 31 July 1989. On 21 July 1989, the Hungarian Government extended the suspension of the works at Nagymaros until 31 October 1989, and, in addition, suspended the works at Dunakiliti until the same date. Lastly, on 27 October 1989, Hungary decided to abandon the works at Nagymaros and to maintain the status quo at Dunakiliti.
    23.
    During this period, negotiations were being held between the parties. Czechoslovakia also started investigating alternative solutions. One of them, subsequently known as "Variant C ", entailed a unilateral diversion of the Danube by Czechoslovakia on its territory some 10 kilometres upstream of Dunakiliti (see sketch-map No. 3, p. 26 below). In its final stage, Variant C included the construction at Cunovo of an overflow dam and a levee linking that dam to the south bank of the bypass canal. The corresponding reservoir was to have a smaller surface area and provide approximately 30 per cent less storage than the reservoir initially contemplated. Provision was made for ancillary works, namely: an intake structure to supply the Mosoni Danube; a weir to enable, inter alia, floodwater to be directed along the old bed of the Danube; an auxiliary shiplock; and two hydroelectric power plants (one capable of an annual production of 4 GWh on the Mosoni Danube, and the other with a production of 174 GWh on the old bed of the Danube). The supply of water to the side-arms of the Danube on the Czechoslovak bank was to be secured by means of two intake structures in the bypass canal at Dobrohost’ and Gabčikovo. A solution was to be found for the Hungarian bank. Moreover, the question of the deepening of the bed of the Danube at the confluence of the bypass canal and the old bed of the river remained outstanding.

    On 23 July 1991, the Slovak Government decided "to begin, in September 1991, construction to put the Gabčikovo Project into operation by the provisional solution". That decision was endorsed by the Federal Czechoslovak Government on 25 July. Work on Variant C began in November 1991. Discussions continued between the two parties but to no avail, and, on 19 May 1992, the Hungarian Government transmitted to the Czechoslovak Government a Note Verbale terminating the 1977 Treaty with effect from 25 May 1992. On 15 October 1992, Czechoslovakia began work to enable the Danube to be closed and, starting on 23 October, proceeded to the damming of the river.

    24.
    On 23 October 1992, the Court was seised of an "Application of the Republic of Hungary v. The Czech and Slovak Federal Republic on the Diversion of the Danube River"; however, Hungary acknowledged that there was no basis on which the Court could have founded its jurisdiction to entertain that application, on which Czechoslovakia took no action. In the meanwhile, the Commission of the European Communities had offered to mediate and, during a meeting of the two parties with the Commission held in London on 28 October 1992, the parties entered into a series of interim undertakings. They principally agreed that the dispute would be submitted to the International Court of Justice, that a tripartite fact-finding mission should report on Variant C not later than 31 October, and that a tripartite group of independent experts would submit suggestions as to emergency measures to be taken.
    25.
    On 1 January 1993 Slovakia became an independent State. On 7 April 1993, the "Special Agreement for Submission to the International Court of Justice of the Differences between the Republic of Hungary and the Slovak Republic concerning the Gabčikovo-Nagymaros Project" was signed in Brussels, the text of which is reproduced in paragraph 2 above. After the Special Agreement was notified to the Court, Hungary informed the Court, by a letter dated 9 August 1993, that it considered its "initial Application [to be] now without object, and... lapsed".

    According to Article 4 of the Special Agreement, "The Parties [agreed] that, pending the final Judgment of the Court, they [would] establish and implement a temporary water management régime for the Danube." However, this régime could not easily be settled. The filling of the Cunovo dam had rapidly led to a major reduction in the flow and in the level of the downstream waters in the old bed of the Danube as well as in the side-arms of the river. On 26 August 1993, Hungary and Slovakia reached agreement on the setting up of a tripartite group of experts (one expert designated by each party and three independent experts designated by the Commission of the European Communities)

    "In order to provide reliable and undisputed data on the most important effects of the current water discharge and the remedial measures already undertaken as well as to make recommendations for appropriate measures."

    On 1 December 1993, the experts designated by the Commission of the European Communities recommended the adoption of various measures to remedy the situation on a temporary basis. The Parties were unable to agree on these recommendations. After lengthy negotiations, they finally concluded an Agreement "concerning Certain Temporary Technical Measures and Discharges in the Danube and Mosoni branch of the Danube", on 19 April 1995. That Agreement raised the discharge of water into the Mosoni Danube to 43 m3/s. It provided for an annual average of 400 m3/s in the old bed (not including flood waters). Lastly, it provided for the construction by Hungary of a partially underwater weir near to Dunakiliti with a view to improving the water supply to the side-arms of the Danube on the Hungarian side. It was specified that this temporary agreement would come to an end 14 days after the Judgment of the Court.

    26.
    The first subparagraph of the Preamble to the Special Agreement covers the disputes arising between Czechoslovakia and Hungary concerning the application and termination, not only of the 1977 Treaty, but also of "related instruments"; the subparagraph specifies that, for the purposes of the Special Agreement, the 1977 Treaty and the said instruments shall be referred to as "the Treaty". "The Treaty" is expressly referred to in the wording of the questions submitted to the Court in Article 2, paragraph 1, subparagraphs (a) and (c), of the Special Agreement.

    The Special Agreement however does not define the concept of "related instruments", nor does it list them. As for the Parties, they gave some consideration to that question — essentially in the written proceedings — without reaching agreement as to the exact meaning of the expression or as to the actual instruments referred to. The Court notes however that the Parties seemed to agree to consider that that expression covers at least the instruments linked to the 1977 Treaty which implement it, such as the Agreement on mutual assistance of 16 September 1977 and its amending Protocols dated, respectively, 10 October 1983 and 6 February 1989 (see paragraph 21 above), and the Agreement as to the common operational regulations of Plenipotentiaries fulfilling duties related to the construction and operation of the Gabčikovo-Nagymaros Barrage System signed in Bratislava on 11 October 1979. The Court notes that Hungary, unlike Slovakia, declined to apply the description of related instruments to the 1977 Treaty to the Joint Contractual Plan (see paragraph 19 above), which it refused to see as "an agreement at the same level as the other... related Treaties and inter-State agreements".

    Lastly the Court notes that the Parties, in setting out the replies which should in their view be given to the questions put in the Special Agreement, concentrated their reasoning on the 1977 Treaty; and that they would appear to have extended their arguments to "related instruments" in considering them as accessories to a whole treaty system, whose fate was in principle linked to that of the main part, the 1977 Treaty. The Court takes note of the positions of the Parties and considers that it does not need to go into this matter further at this juncture.

    27.
    The Court will now turn to a consideration of the questions submitted by the Parties. In terms of Article 2, paragraph 1 (a), of the Special Agreement, the Court is requested to decide first

    "whether the Republic of Hungary was entitled to suspend and subsequently abandon, in 1989, the works on the Nagymaros Project and on the part of the Gabčikovo Project for which the Treaty attributed responsibility to the Republic of Hungary".

    28.
    The Court would recall that the Gabčikovo-Nagymaros System of Locks is characterized in Article 1, paragraph 1, of the 1977 Treaty as a "single and indivisible operational system of works".

    The principal works which were to constitute this system have been described in general terms above (see paragraph 18). Details of them are given in paragraphs 2 and 3 of Article 1 of the Treaty.

    For Gabčikovo, paragraph 2 lists the following works:

    "(a) the Dunakiliti-Hrusov head-water installations in the Danube sector at r.km. (river kilometre(s)) 1860-1842, designed for a maximum flood stage of 131.10 m.B. (metres above sea-level, Baltic system), in Hungarian and Czechoslovak territory;

    (b) the Dunakiliti dam and auxiliary navigation lock at r.km. 1842, in Hungarian territory;

    (c) the by-pass canal (head-water canal and tail-water canal) at r.km. 1842-1811, in Czechoslovak territory;

    (d) series of locks on the by-pass canal, in Czechoslovak territory, consisting of a hydroelectric power plant with installed capacity of 720 MW, double navigation locks and appurtenances thereto ;

    (e) improved old bed of the Danube at r.km. 1842-1811, in the joint Hungarian-Czechoslovak section;

    (f) deepened and regulated bed of the Danube at r.km. 18111791, in the joint Hungarian-Czechoslovak section."

    For Nagymaros, paragraph 3 specifies the following works:

    "(a) head-water installations and flood-control works in the Danube sector at r.km. 1791-1696.25 and in the sectors of tributaries affected by flood waters, designed for a maximum flood stage of 107.83 m.B., in Hungarian and Czechoslovak territory;

    (b) series of locks at r.km. 1696.25, in Hungarian territory, consisting of a dam, a hydroelectric power plant with installed capacity of 158 MW, double navigation locks and appurtenances thereto;

    (c) deepened and regulated bed of the Danube, in both its branches, at r.km. 1696.25-1657, in the Hungarian section."

    29.
    Moreover, the precise breakdown of the works incumbent on each party was set out in Article 5, paragraph 5, of the 1977 Treaty, as follows:

    "5. The labour and supplies required for the realization of the joint investment shall be apportioned between the Contracting Parties in the following manner:

    (a) The Czechoslovak Party shall be responsible for:

    (1) the Dunakiliti-Hrusov head-water installations on the left bank, in Czechoslovak territory;

    (2) the head-water canal of the by-pass canal, in Czechoslovak territory;

    (3) the Gabčikovo series of locks, in Czechoslovak territory ;

    (4) the flood-control works of the Nagymaros head-water installations, in Czechoslovak territory, with the exception of the lower Ipel district ;

    (5) restoration of vegetation in Czechoslovak territory;

    (b) The Hungarian Party shall be responsible for:

    (1) the Dunakiliti-Hrusov head-water installations on the right bank, in Czechoslovak territory, including the connecting weir and the diversionary weir;

    (2) the Dunakiliti-Hrusov head-water installations on the right bank, in Hungarian territory;

    (3) the Dunakiliti dam, in Hungarian territory;

    (4) the tail-water canal of the by-pass canal, in Czechoslovak territory;

    (5) deepening of the bed of the Danube below Palkovicovo, in Hungarian and Czechoslovak territory;

    (6) improvement of the old bed of the Danube, in Hungarian and Czechoslovak territory;

    (7) operational equipment of the Gabčikovo system of locks (transport equipment, maintenance machinery), in Czechoslovak territory;

    (8) the flood-control works of the Nagymaros head-water installations in the lower Ipel district, in Czechoslovak territory;

    (9) the flood-control works of the Nagymaros head-water installations, in Hungarian territory;

    (10) the Nagymaros series of locks, in Hungarian territory;

    (11) deepening of the tail-water bed below the Nagymaros system of locks, in Hungarian territory;

    (12) operational equipment of the Nagymaros system of locks (transport equipment, maintenance machinery), in Hungarian territory;

    (13) restoration of vegetation in Hungarian territory."

    30.
    As the Court has already indicated (see paragraph 18 above), Article 1, paragraph 4, of the 1977 Treaty stipulated in general terms that the "technical specifications" concerning the System of Locks would be included in the "joint contractual plan". The schedule of work had for its part been fixed in an Agreement on mutual assistance signed by the two parties on 16 September 1977 (see paragraph 21 above). In accordance with the provisions of Article 1, paragraph 1, of that Agreement, the whole of the works of the barrage system were to have been completed in 1991. As indicated in paragraph 2 of that same article, a summary construction schedule was appended to the Agreement, and provision was made for a more detailed schedule to be worked out in the Joint Contractual Plan. The Agreement of 16 September 1977 was twice amended further. By a Protocol signed on 10 October 1983, the parties agreed first to postpone the works and the putting into operation of the power plants for four more years; then, by a Protocol signed on 6 February 1989, the parties decided, conversely, to bring them forward by 15 months, the whole system having to be operational in 1994. A new summary construction schedule was appended to each of those Protocols; those schedules were in turn to be implemented by means of new detailed schedules, included in the Joint Contractual Plan.
    31.
    In spring 1989, the work on the Gabčikovo sector was well advanced : the Dunakiliti dam was 90 per cent complete, the Gabčikovo dam was 85 per cent complete, and the bypass canal was between 60 per cent complete (downstream of Gabčikovo) and 95 per cent complete (upstream of Gabčikovo) and the dykes of the Dunakiliti-Hrusov reservoir were between 70 and 98 per cent complete, depending on the location. This was not the case in the Nagymaros sector where, although dykes had been built, the only structure relating to the dam itself was the coffer-dam which was to facilitate its construction.
    32.
    In the wake of the profound political and economic changes which occurred at this time in central Europe, the Gabčikovo-Nagymaros Project was the object, in Czechoslovakia and more particularly in Hungary, of increasing apprehension, both within a section of public opinion and in some scientific circles. The uncertainties not only about the economic viability of the Project, but also, and more so, as to the guarantees it offered for preservation of the environment, engendered a climate of growing concern and opposition with regard to the Project.
    33.
    It was against this background that, on 13 May 1989, the Government of Hungary adopted a resolution to suspend works at Nagymaros, and ordered

    "the Ministers concerned to commission further studies in order to place the Council of Ministers in a position where it can make well-founded suggestions to the Parliament in connection with the amendment of the international treaty on the investment. In the interests of the above, we must examine the international and legal consequences, the technical considerations, the obligations related to continuous navigation on the Danube and the environmental/ecological and seismic impacts of the eventual stopping of the Nagymaros investment. To be further examined are the opportunities for the replacement of the lost electric energy and the procedures for minimising claims for compensation."

    The suspension of the works at Nagymaros was intended to last for the duration of these studies, which were to be completed by 31 July 1989. Czechoslovakia immediately protested and a document defining the position of Czechoslovakia was transmitted to the Ambassador of Hungary in Prague on 15 May 1989. The Prime Ministers of the two countries met on 24 May 1989, but their talks did not lead to any tangible result. On 2 June, the Hungarian Parliament authorized the Government to begin negotiations with Czechoslovakia for the purpose of modifying the 1977 Treaty.

    34.
    At a meeting held by the Plenipotentiaries on 8 and 9 June 1989, Hungary gave Czechoslovakia a number of assurances concerning the continuation of works in the Gabčikovo sector, and the signed Protocol which records that meeting contains the following passage :

    "The Hungarian Government Commissioner and the Hungarian Plenipotentiary stated, that the Hungarian side will complete construction of the Gabčikovo Project in the agreed time and in accordance with the project plans. Directives have already been given to continue works suspended in the area due to misunderstanding."

    These assurances were reiterated in a letter that the Commissioner of the Government of Hungary addressed to the Czechoslovak Plenipotentiary on 9 June 1989.

    35.
    With regard to the suspension of work at Nagymaros, the Hungarian Deputy Prime Minister, in a letter dated 24 June 1989 addressed to his Czechoslovak counterpart, expressed himself in the following terms :

    "The Hungarian Academy of Sciences (HAS) has studied the environmental, ecological and water quality as well as the seismological impacts of abandoning or implementing the Nagymaros Barrage of the Gabčikovo-Nagymaros Barrage System (GNBS).

    Having studied the expected impacts of the construction in accordance with the original plan, the Committee [ad hoc] of the Academy [set up for this purpose] came to the conclusion that we do not have adequate knowledge of the consequences of environmental risks.

    In its opinion, the risk of constructing the Barrage System in accordance with the original plan cannot be considered acceptable. Of course, it cannot be stated either that the adverse impacts will ensue for certain, therefore, according to their recommendation, further thorough and time consuming studies are necessary."

    36.
    The Hungarian and Czechoslovak Prime Ministers met again on 20 July 1989 to no avail. Immediately after that meeting, the Hungarian Government adopted a second resolution, under which the suspension of work at Nagymaros was extended to 31 October 1989. However, this resolution went further, as it also prescribed the suspension, until the same date, of the "Preparatory works on the closure of the riverbed at... Dunakiliti" ; the purpose of this measure was to invite "international scientific institutions [and] foreign scientific institutes and experts" to cooperate with "the Hungarian and Czechoslovak institutes and experts" with a view to an assessment of the ecological impact of the Project and the "development of a technical and operational water quality guarantee system and... its implementation".
    37.
    In the ensuing period, negotiations were conducted at various levels between the two States, but proved fruitless. Finally, by a letter dated 4 October 1989, the Hungarian Prime Minister formally proposed to Czechoslovakia that the Nagymaros sector of the Project be abandoned and that an agreement be concluded with a view to reducing the ecological risks associated with the Gabčikovo sector of the Project. He proposed that that agreement should be concluded before 30 July 1990.

    The two Heads of Government met on 26 October 1989, and were unable to reach agreement. By a Note Verbale dated 30 October 1989, Czechoslovakia, confirming the views it had expressed during those talks, proposed to Hungary that they should negotiate an agreement on a system of technical, operational and ecological guarantees relating to the Gabčikovo-Nagymaros Project, "on the assumption that the Hungarian party will immediately commence preparatory work on the refilling of the Danube’s bed in the region of Dunakiliti". It added that the technical principles of the agreement could be initialled within two weeks and that the agreement itself ought to be signed before the end of March 1990. After the principles had been initialled, Hungary "[was to] start the actual closure of the Danube bed". Czechoslovakia further stated its willingness to "conclu[de]... a separate agreement in which both parties would oblige themselves to limitations or exclusion of peak hour operation mode of the... System". It also proposed "to return to deadlines indicated in the Protocol of October 1983", the Nagymaros construction deadlines being thus extended by 15 months, so as to enable Hungary to take advantage of the time thus gained to study the ecological issues and formulate its own proposals in due time. Czechoslovakia concluded by announcing that, should Hungary continue unilaterally to breach the Treaty, Czechoslovakia would proceed with a provisional solution.

    In the meantime, the Hungarian Government had on 27 October adopted a further resolution, deciding to abandon the construction of the Nagymaros dam and to leave in place the measures previously adopted for suspending the works at Dunakiliti. Then, by Notes Verbales dated 3 and 30 November 1989, Hungary proposed to Czechoslovakia a draft treaty incorporating its earlier proposals, relinquishing peak power operation of the Gabčikovo power plant and abandoning the construction of the Nagymaros dam. The draft provided for the conclusion of an agreement on the completion of Gabčikovo in exchange for guarantees on protection of the environment. It finally envisaged the possibility of one or other party seising an arbitral tribunal or the International Court of Justice in the event that differences of view arose and persisted between the two Governments about the construction and operation of the Gabčikovo dam, as well as measures to be taken to protect the environment. Hungary stated that it was ready to proceed immediately "with the preparatory operations for the Dunakiliti bed-decanting", but specified that the river would not be dammed at Dunakiliti until the agreement on guarantees had been concluded.

    38.
    During winter 1989-1990, the political situation in Czechoslovakia and Hungary alike was transformed, and the new Governments were confronted with many new problems.

    In spring 1990, the new Hungarian Government, in presenting its National Renewal Programme, announced that the whole of the Gabčikovo -Nagymaros Project was a "mistake" and that it would initiate negotiations as soon as possible with the Czechoslovak Government "on remedying and sharing the damages". On 20 December 1990, the Hungarian Government adopted a resolution for the opening of negotiations with Czechoslovakia on the termination of the Treaty by mutual consent and the conclusion of an agreement addressing the consequences of the termination. On 15 February 1991, the Hungarian Plenipotentiary transmitted a draft agreement along those lines to his Czechoslovak counterpart.

    On the same day, the Czechoslovak President declared that the Gabčikovo -Nagymaros Project constituted a "totalitarian, gigomaniac monument which is against nature", while emphasizing that "the problem [was] that [the Gabčikovo power plant] [had] already been built". For his part, the Czechoslovak Minister of the Environment stated, in a speech given to Hungarian parliamentary committees on 11 September 1991, that "the G/N Project [was] an old, obsolete one", but that, if there were "many reasons to change, modify the treaty... it [was] not acceptable to cancel the treaty... and negotiate later on".

    During the ensuing period, Hungary refrained from completing the work for which it was still responsible at Dunakiliti. Yet it continued to maintain the structures it had already built and, at the end of 1991, completed the works relating to the tailrace canal of the bypass canal assigned to it under Article 5, paragraph 5 (b), of the 1977 Treaty.

    39.
    The two Parties to this case concur in recognizing that the 1977 Treaty, the above-mentioned Agreement on mutual assistance of 1977 and the Protocol of 1989 were validly concluded and were duly in force when the facts recounted above took place.

    Further, they do not dispute the fact that, however flexible they may have been, these texts did not envisage the possibility of the signatories unilaterally suspending or abandoning the work provided for therein, or even carrying it out according to a new schedule not approved by the two partners.

    40.
    Throughout the proceedings, Hungary contended that, although it did suspend or abandon certain works, on the contrary, it never suspended the application of the 1977 Treaty itself. To justify its conduct, it relied essentially on a "state of ecological necessity".

    Hungary contended that the various installations in the Gabčikovo-Nagymaros System of Locks had been designed to enable the Gabčikovo power plant to operate in peak mode. Water would only have come through the plant twice each day, at times of peak power demand. Operation in peak mode required the vast expanse (60 km²) of the planned reservoir at Dunakiliti, as well as the Nagymaros dam, which was to alleviate the tidal effects and reduce the variation in the water level downstream of Gabčikovo. Such a system, considered to be more economically profitable than using run-of-the-river plants, carried ecological risks which it found unacceptable.

    According to Hungary, the principal ecological dangers which would have been caused by this system were as follows. At Gabčikovo/ Dunakiliti, under the original Project, as specified in the Joint Contractual Plan, the residual discharge into the old bed of the Danube was limited to 50 m3/s, in addition to the water provided to the system of side-arms. That volume could be increased to 200 m3/s during the growing season. Additional discharges, and in particular a number of artificial floods, could also be effected, at an unspecified rate. In these circumstances, the groundwater level would have fallen in most of the Szigetkoz. Furthermore, the groundwater would then no longer have been supplied by the Danube — which, on the contrary, would have acted as a drain — but by the reservoir of stagnant water at Dunakiliti and the side-arms which would have become silted up. In the long term, the quality of water would have been seriously impaired. As for the surface water, risks of eutrophication would have arisen, particularly in the reservoir; instead of the old Danube there would have been a river choked with sand, where only a relative trickle of water would have flowed. The network of arms would have been for the most part cut off from the principal bed. The fluvial fauna and flora, like those in the alluvial plains, would have been condemned to extinction.

    As for Nagymaros, Hungary argued that, if that dam had been built, the bed of the Danube upstream would have silted up and, consequently, the quality of the water collected in the bank-filtered wells would have deteriorated in this sector. What is more, the operation of the Gabčikovo power plant in peak mode would have occasioned significant daily variations in the water level in the reservoir upstream, which would have constituted a threat to aquatic habitats in particular. Furthermore, the construction and operation of the Nagymaros dam would have caused the erosion of the riverbed downstream, along Szentendre Island. The water level of the river would therefore have fallen in this section and the yield of the bank-filtered wells providing two-thirds of the water supply of the city of Budapest would have appreciably diminished. The filter layer would also have shrunk or perhaps even disappeared, and fine sediments would have been deposited in certain pockets in the river. For this twofold reason, the quality of the infiltrating water would have been severely jeopardized.

    From all these predictions, in support of which it quoted a variety of scientific studies, Hungary concluded that a "state of ecological necessity" did indeed exist in 1989.

    41.
    In its written pleadings, Hungary also accused Czechoslovakia of having violated various provisions of the 1977 Treaty from before 1989 — in particular Articles 15 and 19 relating, respectively, to water quality and nature protection — in refusing to take account of the now evident ecological dangers and insisting that the works be continued, notably at Nagymaros. In this context Hungary contended that, in accordance with the terms of Article 3, paragraph 2, of the Agreement of 6 May 1976 concerning the Joint Contractual Plan, Czechoslovakia bore responsibility for research into the Project’s impact on the environment; Hungary stressed that the research carried out by Czechoslovakia had not been conducted adequately, the potential effects of the Project on the environment of the construction having been assessed by Czechoslovakia only from September 1990. However, in the final stage of its argument, Hungary does not appear to have sought to formulate this complaint as an independent ground formally justifying the suspension and abandonment of the works for which it was responsible under the 1977 Treaty. Rather, it presented the violations of the Treaty prior to 1989, which it imputes to Czechoslovakia, as one of the elements contributing to the emergence of a state of necessity.
    42.
    Hungary moreover contended from the outset that its conduct in the present case should not be evaluated only in relation to the law of treaties. It also observed that, in accordance with the provisions of Article 4, the Vienna Convention of 23 May 1969 on the Law of Treaties could not be applied to the 1977 Treaty, which was concluded before that Convention entered into force as between the parties. Hungary has indeed acknowledged, with reference to the jurisprudence of the Court, that in many respects the Convention reflects the existing customary law. Hungary nonetheless stressed the need to adopt a cautious attitude, while suggesting that the Court should consider, in each case, the conformity of the prescriptions of the Convention with customary international law.
    43.
    Slovakia, for its part, denied that the basis for suspending or abandoning the performance of a treaty obligation can be found outside the law of treaties. It acknowledged that the 1969 Vienna Convention could not be applied as such to the 1977 Treaty, but at the same time stressed that a number of its provisions are a reflection of pre-existing rules of customary international law and specified that this is, in particular, the case with the provisions of Part V relating to invalidity, termination and suspension of the operation of treaties. Slovakia has moreover observed that, after the Vienna Convention had entered into force for both parties, Hungary affirmed its accession to the substantive obligations laid down by the 1977 Treaty when it signed the Protocol of 6 February 1989 that cut short the schedule of work ; and this led it to conclude that the Vienna Convention was applicable to the "contractual legal régime" constituted by the network of interrelated agreements of which the Protocol of 1989 was a part.
    44.
    In the course of the proceedings, Slovakia argued at length that the state of necessity upon which Hungary relied did not constitute a reason for the suspension of a treaty obligation recognized by the law of treaties. At the same time, it cast doubt upon whether "ecological necessity" or "ecological risk" could, in relation to the law of State responsibility, constitute a circumstance precluding the wrongfulness of an act.

    In any event, Slovakia denied that there had been any kind of "ecological state of necessity" in this case either in 1989 or subsequently. It invoked the authority of various scientific studies when it claimed that Hungary had given an exaggeratedly pessimistic description of the situation. Slovakia did not, of course, deny that ecological problems could have arisen. However, it asserted that they could to a large extent have been remedied. It accordingly stressed that no agreement had been reached with respect to the modalities of operation of the Gabčikovo power plant in peak mode, and claimed that the apprehensions of Hungary related only to operating conditions of an extreme kind. In the same way, it contended that the original Project had undergone various modifications since 1977 and that it would have been possible to modify it even further, for example with respect to the discharge of water reserved for the old bed of the Danube, or the supply of water to the side-arms by means of underwater weirs.

    45.
    Slovakia moreover denied that it in any way breached the 1977 Treaty — particularly its Articles 15 and 19 — and maintained, inter alia, that according to the terms of Article 3, paragraph 2, of the Agreement of 6 May 1976 relating to the Joint Contractual Plan, research into the impact of the Project on the environment was not the exclusive responsibility of Czechoslovakia but of either one of the parties, depending on the location of the works.

    Lastly, in its turn, it reproached Hungary with having adopted its unilateral measures of suspension and abandonment of the works in violation of the provisions of Article 27 of the 1977 Treaty (see paragraph 18 above), which it submits required prior recourse to the machinery for dispute settlement provided for in that Article.

    46.
    The Court has no need to dwell upon the question of the applicability in the present case of the Vienna Convention of 1969 on the Law of Treaties. It needs only to be mindful of the fact that it has several times had occasion to hold that some of the rules laid down in that Convention might be considered as a codification of existing customary law. The Court takes the view that in many respects this applies to the provisions of the Vienna Convention concerning the termination and the suspension of the operation of treaties, set forth in Articles 60 to 62 (see Legal Consequences for States of the Continued Presence of South Africa in Namibia (South West Africa) notwithstanding Security Council Resolution 276 (1970), Advisory Opinion, I.C.J. Reports, 1971, p. 47, and Fisheries Jurisdiction (United Kingdom v. Iceland), Jurisdiction of the Court, Judgment, I.C.J. Reports 1973, p. 18; see also Interpretation of the Agreement of 25 March 1951 between the WHO and Egypt, Advisory Opinion, I.C.J. Reports 1980, pp. 95-96).

    Neither has the Court lost sight of the fact that the Vienna Convention is in any event applicable to the Protocol of 6 February 1989 whereby Hungary and Czechoslovakia agreed to accelerate completion of the works relating to the Gabčikovo-Nagymaros Project.

    47.
    Nor does the Court need to dwell upon the question of the relationship between the law of treaties and the law of State responsibility, to which the Parties devoted lengthy arguments, as those two branches of international law obviously have a scope that is distinct. A determination of whether a convention is or is not in force, and whether it has or has not been properly suspended or denounced, is to be made pursuant to the law of treaties. On the other hand, an evaluation of the extent to which the suspension or denunciation of a convention, seen as incompatible with the law of treaties, involves the responsibility of the State which proceeded to it, is to be made under the law of State responsibility.

    Thus the Vienna Convention of 1969 on the Law of Treaties confines itself to defining — in a limitative manner — the conditions in which a treaty may lawfully be denounced or suspended; while the effects of a denunciation or suspension seen as not meeting those conditions are, on the contrary, expressly excluded from the scope of the Convention by operation of Article 73. It is moreover well established that, when a State has committed an internationally wrongful act, its international responsibility is likely to be involved whatever the nature of the obligation it has failed to respect (cf. Interpretation of Peace Treaties with Bulgaria, Hungary and Romania, Second Phase, Advisory Opinion, I.C.J. Reports 1950, p. 228; and see Article 17 of the Draft Articles on State Responsibility provisionally adopted by the International Law Commission on first reading, Yearbook of the International Law Commission, 1980, Vol. II, Part 2, p. 32).

    60.
    By the terms of Article 2, paragraph 1 (b), of the Special Agreement, the Court is asked in the second place to decide

    "(b) whether the Czech and Slovak Federal Republic was entitled to proceed, in November 1991, to the ‘provisional solution’ and to put into operation from October 1992 this system, described in the Report of the Working Group of Independent Experts of the Commission of the European Communities, the Republic of Hungary and the Czech and Slovak Federal Republic dated 23 November 1992 (damming up of the Danube at river kilometre 1851.7 on Czechoslovak territory and resulting consequences on water and navigation course)".

    61.
    The Court will recall that, as soon as Hungary suspended the works at Nagymaros on 13 May 1989 and extended that suspension to certain works to be carried out at Dunakiliti, Czechoslovakia informed Hungary that it would feel compelled to take unilateral measures if Hungary were to persist in its refusal to resume the works. This was inter alia expressed as follows in Czechoslovakia’s Note Verbale of 30 October 1989 to which reference is made in paragraph 37 above:

    "Should the Republic of Hungary fail to meet its liabilities and continue unilaterally to breach the Treaty and related legal documents then the Czechoslovak party will be forced to commence a provisional, substitute project on the territory of the Czechoslovak Socialist Republic in order to prevent further losses. Such a provisional project would entail directing as much water into the Gabčikovo dam as agreed in the Joint Construction Plan."

    As the Court has already indicated (see paragraph 23), various alternative solutions were contemplated by Czechoslovakia. In September 1990, the Hungarian authorities were advised of seven hypothetical alternatives defined by the firm of Hydroconsult of Bratislava. All of those solutions implied an agreement between the parties, with the exception of one variant, subsequently known as "Variant C", which was presented as a provisional solution which could be brought about without Hungarian co-operation. Other contacts between the parties took place, without leading to a settlement of the dispute. In March 1991, Hungary acquired information according to which perceptible progress had been made in finalizing the planning of Variant C; it immediately gave expression to the concern this caused.

    62.
    Inter-governmental negotiation meetings were held on 22 April and 15 July 1991.

    On 22 April 1991, Hungary proposed the suspension, until September 1993, of all the works begun on the basis of the 1977 Treaty, on the understanding that the parties undertook to abstain from any unilateral action, and that joint studies would be carried out in the interval. Czechoslovakia maintained its previous position according to which the studies contemplated should take place within the framework of the 1977 Treaty and without any suspension of the works.

    On 15 July 1991, Czechoslovakia confirmed its intention of putting the Gabčikovo power plant into service and indicated that the available data enabled the effects of four possible scenarios to be assessed, each of them requiring the co-operation of the two Governments. At the same time, it proposed the setting up of a tripartite committee of experts (Hungary, Czechoslovakia, European Communities) which would help in the search for technical solutions to the problems arising from the entry into operation of the Gabčikovo sector. Hungary, for its part, took the view that :

    "In the case of a total lack of understanding the so-called C variation or ‘theoretical opportunity’ suggested by the Czecho-Slovak party as a unilateral solution would be such a grave transgression of Hungarian territorial integrity and International Law for which there is no precedent even in the practices of the formerly socialist countries for the past 30 years";

    it further proposed the setting up of a bilateral committee for the assessment of environmental consequences, subject to work on Czechoslovak territory being suspended.

    63.
    By a letter dated 24 July 1991, the Government of Hungary communicated the following message to the Prime Minister of Slovakia:

    "Hungarian public opinion and the Hungarian Government anxiously and attentively follows the [Czechoslovakian] press reports of the unilateral steps of the Government of the Slovak Republic in connection with the barrage system.

    The preparatory works for diverting the water of the Danube near the Dunakiliti dam through unilaterally are also alarming. These steps are contrary to the 1977 Treaty and to the good relationship between our nations."

    On 30 July 1991 the Slovak Prime Minister informed the Hungarian Prime Minister of

    "the decision of the Slovak Government and of the Czech and Slovak Federal Government to continue work on the Gabčikovo power plant, as a provisional solution, which is aimed at the commencement of operations on the territory of the Czech and Slovak Federal Republic".

    On the same day, the Government of Hungary protested, by a Note Verbale, against the filling of the headrace canal by the Czechoslovak construction company, by pumping water from the Danube.

    By a letter dated 9 August 1991 and addressed to the Prime Minister of Slovakia, the Hungarian authorities strenuously protested against "any unilateral step that would be in contradiction with the interests of our [two] nations and international law" and indicated that they considered it "very important [to] receive information as early as possible on the details of the provisional solution". For its part, Czechoslovakia, in a Note Verbale dated 27 August 1991, rejected the argument of Hungary that the continuation of the works under those circumstances constituted a violation of international law, and made the following proposal:

    "Provided the Hungarian side submits a concrete technical solution aimed at putting into operation the Gabčikovo system of locks and a solution of the system of locks based on the 1977 Treaty in force and the treaty documents related to it, the Czechoslovak side is prepared to implement the mutually agreed solution."

    64.
    The construction permit for Variant C was issued on 30 October 1991. In November 1991 construction of a dam started at Cunovo, where both banks of the Danube are on Czechoslovak (now Slovak) territory.

    In the course of a new inter-governmental negotiation meeting, on 2 December 1991, the parties agreed to entrust the task of studying the whole of the question of the Gabčikovo-Nagymaros Project to a Joint Expert Committee which Hungary agreed should be complemented with an expert from the European Communities. However whereas, for Hungary, the work of that Committee would have been meaningless if Czechoslovakia continued construction of Variant C, for Czechoslovakia, the suspension of the construction, even on a temporary basis, was unacceptable.

    That meeting was followed by a large number of exchanges of letters between the parties and various meetings between their representatives at the end of 1991 and early in 1992. On 23 January 1992, Czechoslovakia expressed its readiness "to stop work on the provisional solution and continue the construction upon mutual agreement" if the tripartite committee of experts whose constitution it proposed, and the results of the test operation of the Gabčikovo part, were to "confirm that negative ecological effects exceed its benefits". However, the positions of the parties were by then comprehensively defined, and would scarcely develop any further. Hungary considered, as it indicated in a Note Verbale of 14 February 1992, that Variant C was in contravention

    "of [the Treaty of 1977]... and the convention ratified in 1976 regarding the water management of boundary waters.

    with the principles of sovereignty, territorial integrity, with the inviolability of State borders, as well as with the general customary norms on international rivers and the spirit of the 1948 Belgrade Danube Convention";

    and the suspension of the implementation of Variant C was, in its view, a prerequisite. As for Czechoslovakia, it took the view that recourse to Variant C had been rendered inevitable, both for economic and ecologi-cal as well as navigational reasons, because of the unlawful suspension and abandonment by Hungary of the works for which provision was made in the 1977 Treaty. Any negotiation had, in its view, to be conducted within the framework of the Treaty and without the implementation of Variant C — described as "provisional" — being called into question.

    65.
    On 5 August 1992, the Czechoslovak representative to the Danube Commission informed it that "work on the severance cutting through of the Danube’s flow will begin on 15 October 1992 at the 1,851,759-kilometre line" and indicated the measures that would be taken at the time of the "severance". The Hungarian representative on the Commission protested on 17 August 1992, and called for additional explanations.

    During the autumn of 1992, the implementation of Variant C was stepped up. The operations involved in damming the Danube at Cunovo had been scheduled by Czechoslovakia to take place during the second half of October 1992, at a time when the waters of the river are generally at their lowest level. On the initiative of the Commission of the European Communities, trilateral negotiations took place in Brussels on 21 and 22 October 1992, with a view to setting up a committee of experts and defining its terms of reference. On that date, the first phase of the operations leading to the damming of the Danube (the reinforcement of the riverbed and the narrowing of the principal channel) had been completed. The closure of the bed was begun on 23 October 1992 and the construction of the actual dam continued from 24 to 27 October 1992: a pontoon bridge was built over the Danube on Czechoslovak territory using river barges, large stones were thrown into the riverbed and reinforced with concrete, while 80 to 90 per cent of the waters of the Danube were directed into the canal designed to supply the Gabčikovo power plant. The implementation of Variant C did not, however, come to an end with the diversion of the waters, as there still remained outstanding both reinforcement work on the dam and the building of certain auxiliary structures.

    The Court has already referred in paragraph 24 to the meeting held in London on 28 October 1992 under the auspices of the European Communities, in the course of which the parties to the negotiations agreed, inter alia, to entrust a tripartite Working Group composed of independent experts (i.e., four experts designated by the European Commission, one designated by Hungary and another by Czechoslovakia) with the task of reviewing the situation created by the implementation of Variant C and making proposals as to urgent measures to adopt. After having worked for one week in Bratislava and one week in Budapest, the Working Group filed its report on 23 November 1992.

    66.
    A summary description of the constituent elements of Variant C appears at paragraph 23 of the present Judgment. For the purposes of the question put to the Court, the official description that should be adopted is, according to Article 2, paragraph 1 (b), of the Special Agreement, the one given in the aforementioned report of the Working Group of independent experts, and it should be emphasized that, according to the Special Agreement, "Variant C" must be taken to include the consequences "on water and navigation course" of the dam closing off the bed of the Danube.

    In the section headed "Variant C Structures and Status of Ongoing Work", one finds, in the report of the Working Group, the following passage :

    "In both countries the original structures for the Gabčikovo scheme are completed except for the closure of the Danube river at Dunakiliti and the

    (1) Completion of the hydropower station (installation and testing of turbines) at Gabčikovo.

    Variant C consists of a complex of structures, located in Czechoslovakia... The construction of these are planned for two phases. The structures include... :

    (2) By-pass weir controlling the flow into the river Danube.

    (3) Dam closing the Danubian river bed.

    (4) Floodplain weir (weir in the inundation).

    (5) Intake structure for the Mosoni Danube.

    (6) Intake structure in the power canal.

    (7) Earth barrages/dykes connecting structures.

    (8) Ship lock for smaller ships (15 m x 80 m).

    (9) Spillway weir.

    (10) Hydropower station.

    The construction of the structures 1-7 are included in Phase 1, while the remaining 8-10 are a part of Phase 2 scheduled for construction 1993-1995."

    67.
    Czechoslovakia had maintained that proceeding to Variant C and putting it into operation did not constitute internationally wrongful acts; Slovakia adopted this argument. During the proceedings before the Court Slovakia contended that Hungary’s decision to suspend and subsequently abandon the construction of works at Dunakiliti had made it impossible for Czechoslovakia to carry out the works as initially contemplated by the 1977 Treaty and that the latter was therefore entitled to proceed with a solution which was as close to the original Project as possible. Slovakia invoked what it described as a "principle of approximate application" to justify the construction and operation of Variant C. It explained that this was the only possibility remaining to it "of fulfilling not only the purposes of the 1977 Treaty, but the continuing obligation to implement it in good faith".
    68.
    Slovakia also maintained that Czechoslovakia was under a duty to mitigate the damage resulting from Hungary’s unlawful actions. It claimed that a State which is confronted with a wrongful act of another State is under an obligation to minimize its losses and, thereby, the damages claimable against the wrongdoing State. It argued furthermore that "Mitigation of damages is also an aspect of the performance of obligations in good faith." For Slovakia, these damages would have been immense in the present case, given the investments made and the additional economic and environmental prejudice which would have resulted from the failure to complete the works at Dunakiliti/Gabčikovo and to put the system into operation. For this reason, Czechoslovakia was not only entitled, but even obliged, to implement Variant C.
    69.
    Although Slovakia maintained that Czechoslovakia’s conduct was lawful, it argued in the alternative that, even were the Court to find otherwise, the putting into operation of Variant C could still be justified as a countermeasure.
    70.
    Hungary for its part contended that Variant C was a material breach of the 1977 Treaty. It considered that Variant C also violated Czechoslovakia’s obligations under other treaties, in particular the Convention of 31 May 1976 on the Regulation of Water Management Issues of Boundary Waters concluded at Budapest, and its obligations under general international law.
    71.
    Hungary contended that Slovakia’s arguments rested on an erroneous presentation of the facts and the law. Hungary denied, inter alia, having committed the slightest violation of its treaty obligations which could have justified the putting into operation of Variant C. It considered that "no such rule" of "approximate application" of a treaty exists in international law; as to the argument derived from "mitigation of damage[s]", it claimed that this has to do with the quantification of loss, and could not serve to excuse conduct which is substantively unlawful. Hungary furthermore stated that Variant C did not satisfy the conditions required by international law for countermeasures, in particular the condition of proportionality.
    72.
    Before dealing with the arguments advanced by the Parties, the Court wishes to make clear that it is aware of the serious problems with which Czechoslovakia was confronted as a result of Hungary’s decision to relinquish most of the construction of the System of Locks for which it was responsible by virtue of the 1977 Treaty. Vast investments had been made, the construction at Gabčikovo was all but finished, the bypass canal was completed, and Hungary itself, in 1991, had duly fulfilled its obligations under the Treaty in this respect in completing work on the tailrace canal. It emerges from the report, dated 31 October 1992, of the tripartite fact-finding mission the Court has referred to in paragraph 24 of the present Judgment, that not using the system would have led to considerable financial losses, and that it could have given rise to serious problems for the environment.
    73.
    Czechoslovakia repeatedly denounced Hungary’s suspension and abandonment of works as a fundamental breach of the 1977 Treaty and consequently could have invoked this breach as a ground for terminating the Treaty; but this would not have brought the Project any nearer to completion. It therefore chose to insist on the implementation of the Treaty by Hungary, and on many occasions called upon the latter to resume performance of its obligations under the Treaty.

    When Hungary steadfastly refused to do so — although it had expressed its willingness to pay compensation for damage incurred by Czechoslovakia — and when negotiations stalled owing to the diametrically opposed positions of the parties, Czechoslovakia decided to put the Gabčikovo system into operation unilaterally, exclusively under its own control and for its own benefit.

    74.
    That decision went through various stages and, in the Special Agreement, the Parties asked the Court to decide whether Czechoslovakia "was entitled to proceed, in November 1991" to Variant C, and "to put [it] into operation from October 1992".
    75.
    With a view to justifying those actions, Slovakia invoked what it described as "the principle of approximate application", expressed by Judge Sir Hersch Lauterpacht in the following terms:

    "It is a sound principle of law that whenever a legal instrument of continuing validity cannot be applied literally owing to the conduct of one of the parties, it must, without allowing that party to take advantage of its own conduct, be applied in a way approximating most closely to its primary object. To do that is to interpret and to give effect to the instrument — not to change it." (Admissibility of Hearings of Petitioners by the Committee on South West Africa, I.C.J. Reports 1956, separate opinion of Sir Hersch Lauterpacht, p. 46.)

    It claimed that this is a principle of international law and a general principle of law.

    76.
    It is not necessary for the Court to determine whether there is a principle of international law or a general principle of law of "approximate application" because, even if such a principle existed, it could by definition only be employed within the limits of the treaty in question. In the view of the Court, Variant C does not meet that cardinal condition with regard to the 1977 Treaty.
    77.
    As the Court has already observed, the basic characteristic of the 1977 Treaty is, according to Article 1, to provide for the construction of the Gabčikovo-Nagymaros System of Locks as a joint investment constituting a single and indivisible operational system of works. This element is equally reflected in Articles 8 and 10 of the Treaty providing for joint ownership of the most important works of the Gabčikovo-Nagymaros Project and for the operation of this joint property as a co-ordinated single unit. By definition all this could not be carried out by unilateral action. In spite of having a certain external physical similarity with the original Project, Variant C thus differed sharply from it in its legal characteristics.
    78.
    Moreover, in practice, the operation of Variant C led Czechoslovakia to appropriate, essentially for its use and benefit, between 80 and 90 per cent of the waters of the Danube before returning them to the main bed of the river, despite the fact that the Danube is not only a shared international watercourse but also an international boundary river.

    Czechoslovakia submitted that Variant C was essentially no more than what Hungary had already agreed to and that the only modifications made were those which had become necessary by virtue of Hungary’s decision not to implement its treaty obligations. It is true that Hungary, in concluding the 1977 Treaty, had agreed to the damming of the Danube and the diversion of its waters into the bypass canal. But it was only in the context of a joint operation and a sharing of its benefits that Hungary had given its consent. The suspension and withdrawal of that consent constituted a violation of Hungary’s legal obligations, demonstrating, as it did, the refusal by Hungary of joint operation; but that cannot mean that Hungary forfeited its basic right to an equitable and reasonable sharing of the resources of an international watercourse.

    The Court accordingly concludes that Czechoslovakia, in putting Variant C into operation, was not applying the 1977 Treaty but, on the contrary, violated certain of its express provisions, and, in so doing, committed an internationally wrongful act.

    81.
    Since the Court has found that the putting into operation of Variant C constituted an internationally wrongful act, the duty to mitigate damage invoked by Slovakia does not need to be examined further.
    88.
    In the light of the conclusions reached above, the Court, in reply to the question put to it in Article 2, paragraph 1 (b), of the Special Agreement (see paragraph 60), finds that Czechoslovakia was entitled to proceed, in November 1991, to Variant C in so far as it then confined itself to undertaking works which did not predetermine the final decision to be taken by it. On the other hand, Czechoslovakia was not entitled to put that Variant into operation from October 1992.
    89.
    By the terms of Article 2, paragraph 1 (c), of the Special Agreement, the Court is asked, thirdly, to determine "what are the legal effects of the notification, on 19 May 1992, of the termination of the Treaty by the Republic of Hungary".

    The Court notes that it has been asked to determine what are the legal effects of the notification given on 19 May 1992 of the termination of the Treaty. It will consequently confine itself to replying to this question.

    90.
    The Court will recall that, by early 1992, the respective parties to the 1977 Treaty had made clear their positions with regard to the recourse by Czechoslovakia to Variant C. Hungary in a Note Verbale of 14 February 1992 had made clear its view that Variant C was a contravention of the 1977 Treaty (see paragraph 64 above); Czechoslovakia insisted on the implementation of Variant C as a condition for further negotiation. On 26 February 1992, in a letter to his Czechoslovak counterpart, the Prime Minister of Hungary described the impending diversion of the Danube as "a serious breach of international law" and stated that, unless work was suspended while further enquiries took place, "the Hungarian Government [would] have no choice but to respond to this situation of necessity by terminating the 1977 inter-State Treaty". In a Note Verbale dated 18 March 1992, Czechoslovakia reaffirmed that, while it was prepared to continue negotiations "on every level", it could not agree "to stop all work on the provisional solution".

    On 24 March 1992, the Hungarian Parliament passed a resolution authorizing the Government to terminate the 1977 Treaty if Czechoslovakia did not stop the works by 30 April 1992. On 13 April 1992, the Vice-President of the Commission of the European Communities wrote to both parties confirming the willingness of the Commission to chair a committee of independent experts including representatives of the two countries, in order to assist the two Governments in identifying a mutually acceptable solution. Commission involvement would depend on each Government not taking "any steps... which would prejudice possible actions to be undertaken on the basis of the report’s findings". The Czechoslovak Prime Minister stated in a letter to the Hungarian Prime Minister dated 23 April 1992, that his Government continued to be interested in the establishment of the proposed committee "without any preliminary conditions" ; criticizing Hungary’s approach, he refused to suspend work on the provisional solution, but added, "in my opinion, there is still time, until the damming of the Danube (i.e., until October 31, 1992), for resolving disputed questions on the basis of agreement of both States".

    On 7 May 1992, Hungary, in the very resolution in which it decided on the termination of the Treaty, made a proposal, this time to the Slovak Prime Minister, for a six-month suspension of work on Variant C. The Slovak Prime Minister replied that the Slovak Government remained ready to negotiate, but considered preconditions "inappropriate".

    91.
    On 19 May 1992, the Hungarian Government transmitted to the Czechoslovak Government a Declaration notifying it of the termination by Hungary of the 1977 Treaty as of 25 May 1992. In a letter of the same date from the Hungarian Prime Minister to the Czechoslovak Prime Minister, the immediate cause for termination was specified to be Czechoslovakia’s refusal, expressed in its letter of 23 April 1992, to suspend the work on Variant C during mediation efforts of the Commission of the European Communities. In its Declaration, Hungary stated that it could not accept the deleterious effects for the environment and the conservation of nature of the implementation of Variant C which would be practically equivalent to the dangers caused by the realization of the original Project. It added that Variant C infringed numerous international agreements and violated the territorial integrity of the Hungarian State by diverting the natural course of the Danube.
    92.
    During the proceedings, Hungary presented five arguments in support of the lawfulness, and thus the effectiveness, of its notification of termination. These were the existence of a state of necessity; the impossibility of performance of the Treaty; the occurrence of a fundamental change of circumstances; the material breach of the Treaty by Czechoslovakia; and, finally, the development of new norms of international environmental law. Slovakia contested each of these grounds.
    93.
    On the first point, Hungary stated that, as Czechoslovakia had "remained inflexible" and continued with its implementation of Variant C, "a temporary state of necessity eventually became permanent, justifying termination of the 1977 Treaty".

    Slovakia, for its part, denied that a state of necessity existed on the basis of what it saw as the scientific facts; and argued that even if such a state of necessity had existed, this would not give rise to a right to terminate the Treaty under the Vienna Convention of 1969 on the Law of Treaties.

    94.
    Hungary’s second argument relied on the terms of Article 61 of the Vienna Convention, which is worded as follows:

    "Article 61

    Supervening Impossibility of Performance

    1. A party may invoke the impossibility of performing a treaty as a ground for terminating or withdrawing from it if the impossibility results from the permanent disappearance or destruction of an object indispensable for the execution of the treaty. If the impossibility is temporary, it may be invoked only as a ground for suspending the operation of the treaty.

    2. Impossibility of performance may not be invoked by a party as a ground for terminating, withdrawing from or suspending the operation of a treaty if the impossibility is the result of a breach by that party either of an obligation under the treaty or of any other international obligation owed to any other party to the treaty."

    Hungary declared that it could not be "obliged to fulfil a practically impossible task, namely to construct a barrage system on its own territory that would cause irreparable environmental damage". It concluded that

    "By May 1992 the essential object of the Treaty — an economic joint investment which was consistent with environmental protection and which was operated by the two parties jointly — had permanently disappeared, and the Treaty had thus become impossible to perform."

    In Hungary’s view, the "object indispensable for the execution of the treaty", whose disappearance or destruction was required by Article 61 of the Vienna Convention, did not have to be a physical object, but could also include, in the words of the International Law Commission, "a legal situation which was the raison d’être of the rights and obligations".

    Slovakia claimed that Article 61 was the only basis for invoking impossibility of performance as a ground for termination, that paragraph 1 of that Article clearly contemplated physical "disappearance or destruction" of the object in question, and that, in any event, paragraph 2 precluded the invocation of impossibility "if the impossibility is the result of a breach by that party... of an obligation under the treaty".

    95.
    As to "fundamental change of circumstances", Hungary relied on Article 62 of the Vienna Convention on the Law of Treaties which states as follows:

    "Article 62

    Fundamental Change of Circumstances

    1. A fundamental change of circumstances which has occurred with regard to those existing at the time of the conclusion of a treaty, and which was not foreseen by the parties, may not be invoked as a ground for terminating or withdrawing from the treaty unless:

    (a) the existence of those circumstances constituted an essential basis of the consent of the parties to be bound by the treaty; and

    (b) the effect of the change is radically to transform the extent of obligations still to be performed under the treaty.

    2. A fundamental change of circumstances may not be invoked as a ground for terminating or withdrawing from a treaty:

    (a) if the treaty establishes a boundary; or

    (b) if the fundamental change is the result of a breach by the party invoking it either of an obligation under the treaty or of any other international obligation owed to any other party to the treaty.

    3. If, under the foregoing paragraphs, a party may invoke a fundamental change of circumstances as a ground for terminating or withdrawing from a treaty it may also invoke the change as a ground for suspending the operation of the treaty."

    Hungary identified a number of "substantive elements" present at the conclusion of the 1977 Treaty which it said had changed fundamentally by the date of notification of termination. These included the notion of "socialist integration", for which the Treaty had originally been a "vehicle", but which subsequently disappeared; the "single and indivisible operational system", which was to be replaced by a unilateral scheme; the fact that the basis of the planned joint investment had been overturned by the sudden emergence of both States into a market economy; the attitude of Czechoslovakia which had turned the "framework treaty" into an "immutable norm"; and, finally, the transformation of a treaty consistent with environmental protection into "a prescription for environmental disaster".

    Slovakia, for its part, contended that the changes identified by Hungary had not altered the nature of the obligations under the Treaty from those originally undertaken, so that no entitlement to terminate it arose from them.

    96.
    Hungary further argued that termination of the Treaty was justified by Czechoslovakia’s material breaches of the Treaty, and in this regard it invoked Article 60 of the Vienna Convention on the Law of Treaties, which provides:

    "Article 60

    Termination or Suspension of the Operation of a Treaty as a Consequence of Its Breach

    1. A material breach of a bilateral treaty by one of the parties entitles the other to invoke the breach as a ground for terminating the treaty or suspending its operation in whole or in part.

    2. A material breach of a multilateral treaty by one of the parties entitles:

    (a) the other parties by unanimous agreement to suspend the operation of the treaty in whole or in part or to terminate it either:

    (i) in the relations between themselves and the defaulting State, or

    (ii) as between all the parties;

    (b) a party specially affected by the breach to invoke it as a ground for suspending the operation of the treaty in whole or in part in the relations between itself and the defaulting State;

    (c) any party other than the defaulting State to invoke the breach as a ground for suspending the operation of the treaty in whole or in part with respect to itself if the treaty is of such a character that a material breach of its provisions by one party radically changes the position of every party with respect to the further performance of its obligations under the treaty.

    3. A material breach of a treaty, for the purposes of this article, consists in:

    (a) a repudiation of the treaty not sanctioned by the present Convention; or

    (b) the violation of a provision essential to the accomplishment of the object or purpose of the treaty.

    4. The foregoing paragraphs are without prejudice to any provision in the treaty applicable in the event of a breach.

    5. Paragraphs 1 to 3 do not apply to provisions relating to the protection of the human person contained in treaties of a humanitarian character, in particular to provisions prohibiting any form of reprisals against persons protected by such treaties."

    Hungary claimed in particular that Czechoslovakia violated the 1977 Treaty by proceeding to the construction and putting into operation of Variant C, as well as failing to comply with its obligations under Articles 15 and 19 of the Treaty. Hungary further maintained that Czechoslovakia had breached other international conventions (among them the Convention of 31 May 1976 on the Regulation of Water Management Issues of Boundary Waters) and general international law.

    Slovakia denied that there had been, on the part of Czechoslovakia or on its part, any material breach of the obligations to protect water quality and nature, and claimed that Variant C, far from being a breach, was devised as "the best possible approximate application" of the Treaty. It furthermore denied that Czechoslovakia had acted in breach of other international conventions or general international law.

    97.
    Finally, Hungary argued that subsequently imposed requirements of international law in relation to the protection of the environment precluded performance of the Treaty. The previously existing obligation not to cause substantive damage to the territory of another State had, Hungary claimed, evolved into an erga omnes obligation of prevention of damage pursuant to the "precautionary principle". On this basis, Hungary argued, its termination was "forced by the other party’s refusal to suspend work on Variant C".

    Slovakia argued, in reply, that none of the intervening developments in environmental law gave rise to norms of jus cogens that would override the Treaty. Further, it contended that the claim by Hungary to be entitled to take action could not in any event serve as legal justification for termination of the Treaty under the law of treaties, but belonged rather "to the language of self-help or reprisals".

    98.
    The question, as formulated in Article 2, paragraph 1 (c), of the Special Agreement, deals with treaty law since the Court is asked to determine what the legal effects are of the notification of termination of the Treaty. The question is whether Hungary’s notification of 19 May 1992 brought the 1977 Treaty to an end, or whether it did not meet the requirements of international law, with the consequence that it did not terminate the Treaty.
    99.
    The Court has referred earlier to the question of the applicability to the present case of the Vienna Convention of 1969 on the Law of Treaties. The Vienna Convention is not directly applicable to the 1977 Treaty inasmuch as both States ratified that Convention only after the Treaty’s conclusion. Consequently only those rules which are declaratory of customary law are applicable to the 1977 Treaty. As the Court has already stated above (see paragraph 46), this is the case, in many respects, with Articles 60 to 62 of the Vienna Convention, relating to termination or suspension of the operation of a treaty. On this, the Parties, too, were broadly in agreement.
    100.
    The 1977 Treaty does not contain any provision regarding its termination. Nor is there any indication that the parties intended to admit the possibility of denunciation or withdrawal. On the contrary, the Treaty establishes a long-standing and durable régime of joint investment and joint operation. Consequently, the parties not having agreed otherwise, the Treaty could be terminated only on the limited grounds enumerated in the Vienna Convention.
    101.
    The Court will now turn to the first ground advanced by Hungary, that of the state of necessity. In this respect, the Court will merely observe that, even if a state of necessity is found to exist, it is not a ground for the termination of a treaty. It may only be invoked to exonerate from its responsibility a State which has failed to implement a treaty. Even if found justified, it does not terminate a Treaty; the Treaty may be ineffective as long as the condition of necessity continues to exist; it may in fact be dormant, but — unless the parties by mutual agreement terminate the Treaty — it continues to exist. As soon as the state of necessity ceases to exist, the duty to comply with treaty obligations revives.
    102.
    Hungary also relied on the principle of the impossibility of performance as reflected in Article 61 of the Vienna Convention on the Law of Treaties. Hungary’s interpretation of the wording of Article 61 is, however, not in conformity with the terms of that Article, nor with the intentions of the Diplomatic Conference which adopted the Convention. Article 61, paragraph 1, requires the "permanent disappearance or destruction of an object indispensable for the execution" of the treaty to justify the termination of a treaty on grounds of impossibility of performance. During the conference, a proposal was made to extend the scope of the article by including in it cases such as the impossibility to make certain payments because of serious financial difficulties (Official Records of the United Nations Conference on the Law of Treaties, First Session, Vienna, 26 March-24 May 1968, doc. A/CONF.39/11, Summary records of the plenary meetings and of the meetings of the Committee of the Whole, 62nd Meeting of the Committee of the Whole, pp. 361-365). Although it was recognized that such situations could lead to a preclusion of the wrongfulness of non-performance by a party of its treaty obligations, the participating States were not prepared to consider such situations to be a ground for terminating or suspending a treaty, and preferred to limit themselves to a narrower concept.
    103.
    Hungary contended that the essential object of the Treaty — an economic joint investment which was consistent with environmental protection and which was operated by the two contracting parties jointly — had permanently disappeared and that the Treaty had thus become impossible to perform. It is not necessary for the Court to determine whether the term "object" in Article 61 can also be understood to embrace a legal régime as in any event, even if that were the case, it would have to conclude that in this instance that régime had not definitively ceased to exist. The 1977 Treaty — and in particular its Articles 15, 19 and 20 — actually made available to the parties the necessary means to proceed at any time, by negotiation, to the required readjustments between economic imperatives and ecological imperatives. The Court would add that, if the joint exploitation of the investment was no longer possible, this was originally because Hungary did not carry out most of the works for which it was responsible under the 1977 Treaty; Article 61, paragraph 2, of the Vienna Convention expressly provides that impossibility of performance may not be invoked for the termination of a treaty by a party to that treaty when it results from that party’s own breach of an obligation flowing from that treaty.
    105.
    The Court will now examine Hungary’s argument that it was entitled to terminate the 1977 Treaty on the ground that Czechoslovakia had violated its Articles 15, 19 and 20 (as well as a number of other conventions and rules of general international law); and that the planning, construction and putting into operation of Variant C also amounted to a material breach of the 1977 Treaty.
    106.
    As to that part of Hungary’s argument which was based on other treaties and general rules of international law, the Court is of the view that it is only a material breach of the treaty itself, by a State party to that treaty, which entitles the other party to rely on it as a ground for terminating the treaty. The violation of other treaty rules or of rules of general international law may justify the taking of certain measures, including countermeasures, by the injured State, but it does not constitute a ground for termination under the law of treaties.
    107.
    Hungary contended that Czechoslovakia had violated Articles 15, 19 and 20 of the Treaty by refusing to enter into negotiations with Hungary in order to adapt the Joint Contractual Plan to new scientific and legal developments regarding the environment. Articles 15, 19 and 20 oblige the parties jointly to take, on a continuous basis, appropriate measures necessary for the protection of water quality, of nature and of fishing interests.

    Articles 15 and 19 expressly provide that the obligations they contain shall be implemented by the means specified in the Joint Contractual Plan. The failure of the parties to agree on those means cannot, on the basis of the record before the Court, be attributed solely to one party. The Court has not found sufficient evidence to conclude that Czechoslovakia had consistently refused to consult with Hungary about the desirability or necessity of measures for the preservation of the environment. The record rather shows that, while both parties indicated, in principle, a willingness to undertake further studies, in practice Czechoslovakia refused to countenance a suspension of the works at Dunakiliti and, later, on Variant C, while Hungary required suspension as a prior condition of environmental investigation because it claimed continuation of the work would prejudice the outcome of negotiations. In this regard it cannot be left out of consideration that Hungary itself, by suspending the works at Nagymaros and Dunakiliti, contributed to the creation of a situation which was not conducive to the conduct of fruitful negotiations.

    108.
    Hungary’s main argument for invoking a material breach of the Treaty was the construction and putting into operation of Variant C. As the Court has found in paragraph 79 above, Czechoslovakia violated the Treaty only when it diverted the waters of the Danube into the bypass canal in October 1992. In constructing the works which would lead to the putting into operation of Variant C, Czechoslovakia did not act unlawfully.

    In the Court’s view, therefore, the notification of termination by Hungary on 19 May 1992 was premature. No breach of the Treaty by Czechoslovakia had yet taken place and consequently Hungary was not entitled to invoke any such breach of the Treaty as a ground for terminating it when it did.

    109.
    In this regard, it should be noted that, according to Hungary’s Declaration of 19 May 1992, the termination of the 1977 Treaty was to take effect as from 25 May 1992, that is only six days later. Both Parties agree that Articles 65 to 67 of the Vienna Convention on the Law of Treaties, if not codifying customary law, at least generally reflect customary international law and contain certain procedural principles which are based on an obligation to act in good faith. As the Court stated in its Advisory Opinion on the Interpretation of the Agreement of 25 March 1951 between the WHO and Egypt (in which case the Vienna Convention did not apply):

    "Precisely what periods of time may be involved in the observance of the duties to consult and negotiate, and what period of notice of termination should be given, are matters which necessarily vary according to the requirements of the particular case. In principle, therefore, it is for the parties in each case to determine the length of those periods by consultation and negotiation in good faith." (I.C.J. Reports 1980, p. 96, para. 49.)

    The termination of the Treaty by Hungary was to take effect six days after its notification. On neither of these dates had Hungary suffered injury resulting from acts of Czechoslovakia. The Court must therefore confirm its conclusion that Hungary’s termination of the Treaty was premature.

    111.
    Finally, the Court will address Hungary’s claim that it was entitled to terminate the 1977 Treaty because new requirements of international law for the protection of the environment precluded performance of the Treaty.
    112.
    Neither of the Parties contended that new peremptory norms of environmental law had emerged since the conclusion of the 1977 Treaty, and the Court will consequently not be required to examine the scope of Article 64 of the Vienna Convention on the Law of Treaties. On the other hand, the Court wishes to point out that newly developed norms of environmental law are relevant for the implementation of the Treaty and that the parties could, by agreement, incorporate them through the application of Articles 15, 19 and 20 of the Treaty. These articles do not contain specific obligations of performance but require the parties, in carrying out their obligations to ensure that the quality of water in the Danube is not impaired and that nature is protected, to take new environmental norms into consideration when agreeing upon the means to be specified in the Joint Contractual Plan.

    By inserting these evolving provisions in the Treaty, the parties recognized the potential necessity to adapt the Project. Consequently, the Treaty is not static, and is open to adapt to emerging norms of international law. By means of Articles 15 and 19, new environmental norms can be incorporated in the Joint Contractual Plan.

    The responsibility to do this was a joint responsibility. The obligations contained in Articles 15, 19 and 20 are, by definition, general and have to be transformed into specific obligations of performance through a process of consultation and negotiation. Their implementation thus requires a mutual willingness to discuss in good faith actual and potential environmental risks.

    It is all the more important to do this because as the Court recalled in its Advisory Opinion on the Legality of the Threat or Use of Nuclear Weapons, "the environment is not an abstraction but represents the living space, the quality of life and the very health of human beings, including generations unborn" (I.C.J. Reports 1996, p. 241, para. 29; see also paragraph 53 above).

    The awareness of the vulnerability of the environment and the recognition that environmental risks have to be assessed on a continuous basis have become much stronger in the years since the Treaty’s conclusion. These new concerns have enhanced the relevance of Articles 15, 19 and 20.

    113.
    The Court recognizes that both Parties agree on the need to take environmental concerns seriously and to take the required precautionary measures, but they fundamentally disagree on the consequences this has for the joint Project. In such a case, third-party involvement may be helpful and instrumental in finding a solution, provided each of the Parties is flexible in its position.
    114.
    Finally, Hungary maintained that by their conduct both parties had repudiated the Treaty and that a bilateral treaty repudiated by both parties cannot survive. The Court is of the view, however, that although it has found that both Hungary and Czechoslovakia failed to comply with their obligations under the 1977 Treaty, this reciprocal wrongful conduct did not bring the Treaty to an end nor justify its termination. The Court would set a precedent with disturbing implications for treaty relations and the integrity of the rule pacta sunt servanda if it were to conclude that a treaty in force between States, which the parties have implemented in considerable measure and at great cost over a period of years, might be unilaterally set aside on grounds of reciprocal noncompliance. It would be otherwise, of course, if the parties decided to terminate the Treaty by mutual consent. But in this case, while Hungary purported to terminate the Treaty, Czechoslovakia consistently resisted this act and declared it to be without legal effect.
    115.
    In the light of the conclusions it has reached above, the Court, in reply to the question put to it in Article 2, paragraph 1 (c),of the Special Agreement (see paragraph 89), finds that the notification of termination by Hungary of 19 May 1992 did not have the legal effect of terminating the 1977 Treaty and related instruments.
    116.
    In Article 2, paragraph 2, of the Special Agreement, the Court is requested to determine the legal consequences, including the rights and obligations for the Parties, arising from its Judgment on the questions formulated in paragraph 1. In Article 5 of the Special Agreement the Parties agreed to enter into negotiations on the modalities for the execution of the Judgment immediately after the Court has rendered it.
    117.
    The Court must first turn to the question whether Slovakia became a party to the 1977 Treaty as successor to Czechoslovakia. As an alternative argument, Hungary contended that, even if the Treaty survived the notification of termination, in any event it ceased to be in force as a treaty on 31 December 1992, as a result of the "disappearance of one of the parties". On that date Czechoslovakia ceased to exist as a legal entity, and on 1 January 1993 the Czech Republic and the Slovak Republic came into existence.
    118.
    According to Hungary, "There is no rule of international law which provides for automatic succession to bilateral treaties on the disappearance of a party" and such a treaty will not survive unless another State succeeds to it by express agreement between that State and the remaining party. While the second paragraph of the Preamble to the Special Agreement recites that

    "the Slovak Republic is one of the two successor States of the Czech and Slovak Federal Republic and the sole successor State in respect of rights and obligations relating to the Gabčikovo-Nagymaros Project",

    Hungary sought to distinguish between, on the one hand, rights and obligations such as "continuing property rights" under the 1977 Treaty, and, on the other hand, the treaty itself. It argued that, during the negotiations leading to signature of the Special Agreement, Slovakia had proposed a text in which it would have been expressly recognized "as the successor to the Government of the CSFR" with regard to the 1977 Treaty, but that Hungary had rejected that formulation. It contended that it had never agreed to accept Slovakia as successor to the 1977 Treaty. Hungary referred to diplomatic exchanges in which the two Parties had each submitted to the other lists of those bilateral treaties which they respectively wished should continue in force between them, for negotiation on a case-by-case basis; and Hungary emphasized that no agreement was ever reached with regard to the 1977 Treaty.

    119.
    Hungary claimed that there was no rule of succession which could operate in the present case to override the absence of consent.

    Referring to Article 34 of the Vienna Convention of 23 August 1978 on Succession of States in respect of Treaties, in which "a rule of automatic succession to all treaties is provided for", based on the principle of continuity, Hungary argued not only that it never signed or ratified the Convention, but that the "concept of automatic succession" contained in that Article was not and is not, and has never been accepted as, a statement of general international law.

    Hungary further submitted that the 1977 Treaty did not create "obligations and rights... relating to the régime of a boundary" within the meaning of Article 11 of that Convention, and noted that the existing course of the boundary was unaffected by the Treaty. It also denied that the Treaty was a "localized" treaty, or that it created rights "considered as attaching to [the] territory" within the meaning of Article 12 of the 1978 Convention, which would, as such, be unaffected by a succession of States. The 1977 Treaty was, Hungary insisted, simply a joint investment. Hungary’s conclusion was that there is no basis on which the Treaty could have survived the disappearance of Czechoslovakia so as to be binding as between itself and Slovakia.

    120.
    According to Slovakia, the 1977 Treaty, which was not lawfully terminated by Hungary’s notification in May 1992, remains in force between itself, as successor State, and Hungary.

    Slovakia acknowledged that there was no agreement on succession to the Treaty between itself and Hungary. It relied instead, in the first place, on the "general rule of continuity which applies in the case of dissolution"; it argued, secondly, that the Treaty is one "attaching to [the] territory" within the meaning of Article 12 of the 1978 Vienna Convention, and that it contains provisions relating to a boundary.

    121.
    In support of its first argument Slovakia cited Article 34 of the 1978 Vienna Convention, which it claimed is a statement of customary international law, and which imposes the principle of automatic succession as the rule applicable in the case of dissolution of a State where the predecessor State has ceased to exist. Slovakia maintained that State practice in cases of dissolution tends to support continuity as the rule to be followed with regard to bilateral treaties. Slovakia having succeeded to part of the territory of the former Czechoslovakia, this would be the rule applicable in the present case.
    122.
    Slovakia’s second argument rests on "the principle of ipso jure continuity of treaties of a territorial or localized character". This rule, Slovakia said, is embodied in Article 12 of the 1978 Convention, which in part provides as follows:

    "Article 12

    Other Territorial Regimes

    2. A succession of States does not as such affect:

    (a) obligations relating to the use of any territory, or to restrictions upon its use, established by a treaty for the benefit of a group of States or of all States and considered as attaching to that territory;

    (b) rights established by a treaty for the benefit of a group of States or of all States and relating to the use of any territory, or to restrictions upon its use, and considered as attaching to that territory."

    According to Slovakia, "[this] article [too] can be considered to be one of those provisions of the Vienna Convention that represent the codification of customary international law". The 1977 Treaty is said to fall within its scope because of its "specific characteristics... which place it in the category of treaties of a localized or territorial character". Slovakia also described the Treaty as one "which contains boundary provisions and lays down a specific territorial régime" which operates in the interest of all Danube riparian States, and as "a dispositive treaty, creating rights in rem, independently of the legal personality of its original signatories". Here, Slovakia relied on the recognition by the International Law Commission of the existence of a "special rule" whereby treaties "intended to establish an objective régime" must be considered as binding on a successor State (Official Records of the United Nations Conference on the Succession of States in respect of Treaties, Vol. III, doc. A/CONF.80/16/ Add.2, p. 34). Thus, in Slovakia’s view, the 1977 Treaty was not one which could have been terminated through the disappearance of one of the original parties.

    123.
    The Court does not find it necessary for the purposes of the present case to enter into a discussion of whether or not Article 34 of the 1978 Convention reflects the state of customary international law. More relevant to its present analysis is the particular nature and character of the 1977 Treaty. An examination of this Treaty confirms that, aside from its undoubted nature as a joint investment, its major elements were the proposed construction and joint operation of a large, integrated and indivisible complex of structures and installations on specific parts of the respective territories of Hungary and Czechoslovakia along the Danube. The Treaty also established the navigational régime for an important sector of an international waterway, in particular the relocation of the main international shipping lane to the bypass canal. In so doing, it inescapably created a situation in which the interests of other users of the Danube were affected. Furthermore, the interests of third States were expressly acknowledged in Article 18, whereby the parties undertook to ensure "uninterrupted and safe navigation on the international fairway" in accordance with their obligations under the Convention of 18 August 1948 concerning the Régime of Navigation on the Danube.

    In its Commentary on the Draft Articles on Succession of States in respect of Treaties, adopted at its twenty-sixth session, the International Law Commission identified "treaties of a territorial character" as having been regarded both in traditional doctrine and in modern opinion as unaffected by a succession of States (Official Records of the United Nations Conference on the Succession of States in respect of Treaties, Vol. III, doc. A/CONF.80/16/Add.2, p. 27, para. 2). The draft text of Article 12, which reflects this principle, was subsequently adopted unchanged in the 1978 Vienna Convention. The Court considers that Article 12 reflects a rule of customary international law; it notes that neither of the Parties disputed this. Moreover, the Commission indicated that "treaties concerning water rights or navigation on rivers are commonly regarded as candidates for inclusion in the category of territorial treaties" (ibid., p. 33, para. 26). The Court observes that Article 12, in providing only, without reference to the treaty itself, that rights and obligations of a territorial character established by a treaty are unaffected by a succession of States, appears to lend support to the position of Hungary rather than of Slovakia. However the Court concludes that this formulation was devised rather to take account of the fact that, in many cases, treaties which had established boundaries or territorial régimes were no longer in force (ibid., pp. 26-37). Those that remained in force would nonetheless bind a successor State.

    Taking all these factors into account, the Court finds that the content of the 1977 Treaty indicates that it must be regarded as establishing a territorial régime within the meaning of Article 12 of the 1978 Vienna Convention. It created rights and obligations "attaching to" the parts of the Danube to which it relates; thus the Treaty itself cannot be affected by a succession of States. The Court therefore concludes that the 1977 Treaty became binding upon Slovakia on 1 January 1993.

    124.
    It might be added that Slovakia also contended that, while still a constituent part of Czechoslovakia, it played a role in the development of the Project, as it did later, in the most critical phase of negotiations with Hungary about the fate of the Project. The evidence shows that the Slovak Government passed resolutions prior to the signing of the 1977 Treaty in preparation for its implementation; and again, after signature, expressing its support for the Treaty. It was the Slovak Prime Minister who attended the meeting held in Budapest on 22 April 1991 as the Plenipotentiary of the Federal Government to discuss questions arising out of the Project. It was his successor as Prime Minister who notified his Hungarian counterpart by letter on 30 July 1991 of the decision of the Government of the Slovak Republic, as well as of the Government of the Czech and Slovak Federal Republic, to proceed with the "provisional solution" (see paragraph 63 above); and who wrote again on 18 December 1991 to the Hungarian Minister without Portfolio, renewing an earlier suggestion that a joint commission be set up under the auspices of the European Communities to consider possible solutions. The Slovak Prime Minister also wrote to the Hungarian Prime Minister in May 1992 on the subject of the decision taken by the Hungarian Government to terminate the Treaty, informing him of resolutions passed by the Slovak Government in response.

    It is not necessary, in the light of the conclusions reached in paragraph 123 above, for the Court to determine whether there are legal consequences to be drawn from the prominent part thus played by the Slovak Republic. Its role does, however, deserve mention.

    125.
    The Court now turns to the other legal consequences arising from its Judgment.

    As to this, Hungary argued that future relations between the Parties, as far as Variant C is concerned, are not governed by the 1977 Treaty. It claims that it is entitled, pursuant to the Convention of 1976 on the Regulation of Water Management Issues of Boundary Waters, to "50% of the natural flow of the Danube at the point at which it crosses the boundary below Cunovo" and considers that the Parties

    "are obliged to enter into negotiations in order to produce the result that the water conditions along the area from below Cunovo to below the confluence at Sap become jointly defined water conditions as required by Article 3 (a) of the 1976 Convention".

    Hungary moreover indicated that any mutually accepted long-term discharge régime must be "capable of avoiding damage, including especially damage to biodiversity prohibited by the [1992 Rio Convention on Biological Diversity]". It added that "a joint environmental impact assessment of the region and of the future of Variant C structures in the context of the sustainable development of the region" should be carried out.

    126.
    Hungary also raised the question of financial accountability for the failure of the original project and stated that both Parties accept the fact that the other has "proprietary and financial interests in the residues of the original Project and that an accounting has to be carried out". Furthermore, it noted that:

    "Other elements of damage associated with Variant C on Hungarian territory also have to be brought into the accounting..., as well as electricity production since the diversion",

    and that: "The overall situation is a complex one, and it may be most easily resolved by some form of lump sum settlement."

    127.
    Hungary stated that Slovakia had incurred international responsibility and should make reparation for the damage caused to Hungary by the operation of Variant C. In that connection, it referred, in the context of reparation of the damage to the environment, to the rule of restitutio in integrum, and called for the re-establishment of "joint control by the two States over the installations maintained as they are now", and the "re-establishment of the flow of [the] waters to the level at which it stood prior to the unlawful diversion of the river". It also referred to reparation of the damage to the fauna, the flora, the soil, the sub-soil, the groundwater and the aquifer, the damages suffered by the Hungarian population on account of the increase in the uncertainties weighing on its future (pretium doloris), and the damage arising from the unlawful use, in order to divert the Danube, of installations over which the two Parties exercised joint ownership.

    Lastly, Hungary called for the "cessation of the continuous unlawful acts" and a "guarantee that the same actions will not be repeated", and asked the Court to order "the permanent suspension of the operation of Variant C".

    128.
    Slovakia argued for its part that Hungary should put an end to its unlawful conduct and cease to impede the application of the 1977 Treaty, taking account of its "flexibility and of the important possibilities of development for which it provides, or even of such amendments as might be made to it by agreement between the Parties, further to future negotiations". It stated that joint operations could resume on a basis jointly agreed upon and emphasized the following:

    "whether Nagymaros is built as originally planned, or built elsewhere in a different form, or, indeed, not built at all, is a question to be decided by the Parties some time in the future.

    Provided the bypass canal and the Gabčikovo Power-station and Locks — both part of the original Treaty, and not part of Variant C — remain operational and economically viable and efficient, Slovakia is prepared to negotiate over the future roles of Dunakiliti and Cunovo, bearing Nagymaros in mind."

    It indicated that the Gabčikovo power plant would not operate in peak mode "if the evidence of environmental damage [was] clear and accepted by both Parties". Slovakia noted that the Parties appeared to agree that an accounting should be undertaken "so that, guided by the Court’s findings on responsibility, the Parties can try to reach a global settlement". It added that the Parties would have to agree on how the sums due are to be paid.

    129.
    Slovakia stated that Hungary must make reparation for the deleterious consequences of its failures to comply with its obligations, "whether they relate to its unlawful suspensions and abandonments of works or to its formal repudiation of the Treaty as from May 1992", and that compensation should take the form of a restitutio in integrum. It indicated that "Unless the Parties come to some other arrangement by concluding an agreement, restitutio in integrum ought to take the form of a return by Hungary, at a future time, to its obligations under the Treaty" and that "For compensation to be ‘full’..., to ‘wipe out all the consequences of the illegal act’..., a payment of compensation must... be added to the restitutio...." Slovakia claims compensation which must include both interest and loss of profits and should cover the following heads of damage, which it offers by way of guidance:

    (1) Losses caused to Slovakia in the Gabčikovo sector: costs incurred from 1990 to 1992 by Czechoslovakia in protecting the structures of the G/N project and adjacent areas; the cost of maintaining the old bed of the River Danube pending the availability of the new navigation canal, from 1990 to 1992; losses to the Czechoslovak navigation authorities due to the unavailability of the bypass canal from 1990 to 1992; construction costs of Variant C (1990-1992).

    (2) Losses caused to Slovakia in the Nagymaros sector: losses in the field of navigation and flood protection incurred since 1992 by Slovakia due to the failure of Hungary to proceed with the works.

    (3) Loss of electricity production.

    Slovakia also calls for Hungary to "give the appropriate guarantees that it will abstain from preventing the application of the Treaty and the continuous operation of the system". It argued from that standpoint that it is entitled "to be given a formal assurance that the internationally wrongful acts of Hungary will not recur", and it added that "the maintenance of the closure of the Danube at Cunovo constitutes a guarantee of that kind", unless Hungary gives an equivalent guarantee "within the framework of the negotiations that are to take place between the Parties".

    130.
    The Court observes that the part of its Judgment which answers the questions in Article 2, paragraph 1, of the Special Agreement has a declaratory character. It deals with the past conduct of the Parties and determines the lawfulness or unlawfulness of that conduct between 1989 and 1992 as well as its effects on the existence of the Treaty.
    131.
    Now the Court has, on the basis of the foregoing findings, to determine what the future conduct of the Parties should be. This part of the Judgment is prescriptive rather than declaratory because it determines what the rights and obligations of the Parties are. The Parties will have to seek agreement on the modalities of the execution of the Judgment in the light of this determination, as they agreed to do in Article 5 of the Special Agreement.
    132.
    In this regard it is of cardinal importance that the Court has found that the 1977 Treaty is still in force and consequently governs the relationship between the Parties. That relationship is also determined by the rules of other relevant conventions to which the two States are party, by the rules of general international law and, in this particular case, by the rules of State responsibility; but it is governed, above all, by the applicable rules of the 1977 Treaty as a lex specialis.
    134.
    What might have been a correct application of the law in 1989 or 1992, if the case had been before the Court then, could be a miscarriage of justice if prescribed in 1997. The Court cannot ignore the fact that the Gabčikovo power plant has been in operation for nearly five years, that the bypass canal which feeds the plant receives its water from a significantly smaller reservoir formed by a dam which is built not at Dunakiliti but at Cunovo, and that the plant is operated in a run-of-the-river mode and not in a peak hour mode as originally foreseen. Equally, the Court cannot ignore the fact that, not only has Nagymaros not been built, but that, with the effective discarding by both Parties of peak power operation, there is no longer any point in building it.
    135.
    As the Court has already had occasion to point out, the 1977 Treaty was not only a joint investment project for the production of energy, but it was designed to serve other objectives as well : the improvement of the navigability of the Danube, flood control and regulation of ice-discharge, and the protection of the natural environment. None of these objectives has been given absolute priority over the other, in spite of the emphasis which is given in the Treaty to the construction of a System of Locks for the production of energy. None of them has lost its importance. In order to achieve these objectives the parties accepted obligations of conduct, obligations of performance, and obligations of result.
    136.
    It could be said that that part of the obligations of performance which related to the construction of the System of Locks — in so far as they were not yet implemented before 1992 — have been overtaken by events. It would be an administration of the law altogether out of touch with reality if the Court were to order those obligations to be fully reinstated and the works at Cunovo to be demolished when the objectives of the Treaty can be adequately served by the existing structures.
    137.
    Whether this is indeed the case is, first and foremost, for the Parties to decide. Under the 1977 Treaty its several objectives must be attained in an integrated and consolidated programme, to be developed in the Joint Contractual Plan. The Joint Contractual Plan was, until 1989, adapted and amended frequently to better fit the wishes of the parties. This Plan was also expressly described as the means to achieve the objectives of maintenance of water quality and protection of the environment.
    138.
    The 1977 Treaty never laid down a rigid system, albeit that the construction of a system of locks at Gabčikovo and Nagymaros was prescribed by the Treaty itself. In this respect, however, the subsequent positions adopted by the parties should be taken into consideration. Not only did Hungary insist on terminating construction at Nagymaros, but Czechoslovakia stated, on various occasions in the course of negotiations, that it was willing to consider a limitation or even exclusion of operation in peak hour mode. In the latter case the construction of the Nagymaros dam would have become pointless. The explicit terms of the Treaty itself were therefore in practice acknowledged by the parties to be negotiable.
    139.
    The Court is of the opinion that the Parties are under a legal obligation, during the negotiations to be held by virtue of Article 5 of the Special Agreement, to consider, within the context of the 1977 Treaty, in what way the multiple objectives of the Treaty can best be served, keeping in mind that all of them should be fulfilled.
    142.
    What is required in the present case by the rule pacta sunt servanda, as reflected in Article 26 of the Vienna Convention of 1969 on the Law of Treaties, is that the Parties find an agreed solution within the cooperative context of the Treaty.

    Article 26 combines two elements, which are of equal importance. It provides that "Every treaty in force is binding upon the parties to it and must be performed by them in good faith." This latter element, in the Court’s view, implies that, in this case, it is the purpose of the Treaty, and the intentions of the parties in concluding it, which should prevail over its literal application. The principle of good faith obliges the Parties to apply it in a reasonable way and in such a manner that its purpose can be realized.

    143.
    During this dispute both Parties have called upon the assistance of the Commission of the European Communities. Because of the diametrically opposed positions the Parties took with regard to the required outcome of the trilateral talks which were envisaged, those talks did not succeed. When, after the present Judgment is given, bilateral negotiations without pre-conditions are held, both Parties can profit from the assistance and expertise of a third party. The readiness of the Parties to accept such assistance would be evidence of the good faith with which they conduct bilateral negotiations in order to give effect to the Judgment of the Court.
    144.
    The 1977 Treaty not only contains a joint investment programme, it also establishes a régime. According to the Treaty, the main structures of the System of Locks are the joint property of the Parties; their operation will take the form of a co-ordinated single unit; and the benefits of the project shall be equally shared.

    Since the Court has found that the Treaty is still in force and that, under its terms, the joint régime is a basic element, it considers that, unless the Parties agree otherwise, such a régime should be restored.

    145.
    Article 10, paragraph 1, of the Treaty states that works of the System of Locks constituting the joint property of the contracting parties shall be operated, as a co-ordinated single unit and in accordance with jointly agreed operating and operational procedures, by the authorized operating agency of the contracting party in whose territory the works are built. Paragraph 2 of that Article states that works on the System of Locks owned by one of the contracting parties shall be independently operated or maintained by the agencies of that contracting party in the jointly prescribed manner.

    The Court is of the opinion that the works at Cunovo should become a jointly operated unit within the meaning of Article 10, paragraph 1, in view of their pivotal role in the operation of what remains of the Project and for the water-management régime. The dam at Cunovo has taken over the role which was originally destined for the works at Dunakiliti, and therefore should have a similar status.

    146.
    The Court also concludes that Variant C, which it considers operates in a manner incompatible with the Treaty, should be made to conform to it. By associating Hungary, on an equal footing, in its operation, management and benefits, Variant C will be transformed from a de facto status into a treaty-based régime.

    It appears from various parts of the record that, given the current state of information before the Court, Variant C could be made to function in such a way as to accommodate both the economic operation of the system of electricity generation and the satisfaction of essential environmental concerns.

    Regularization of Variant C by making it part of a single and indivisible operational system of works also appears necessary to ensure that Article 9 of the Treaty, which provides that the contracting parties shall participate in the use and in the benefits of the System of Locks in equal measure, will again become effective.

    147.
    Re-establishment of the joint régime will also reflect in an optimal way the concept of common utilization of shared water resources for the achievement of the several objectives mentioned in the Treaty, in concordance with Article 5, paragraph 2, of the Convention on the Law of the Non-Navigational Uses of International Watercourses, according to which :

    "Watercourse States shall participate in the use, development and protection of an international watercourse in an equitable and reasonable manner. Such participation includes both the right to utilize the watercourse and the duty to cooperate in the protection and development thereof, as provided in the present Convention." (General Assembly doc. A/51/869 of 11 April 1997.)

    151.
    The Court has been asked by both Parties to determine the consequences of the Judgment as they bear upon payment of damages. According to the Preamble to the Special Agreement, the Parties agreed that Slovakia is the sole successor State of Czechoslovakia in respect of rights and obligations relating to the Gabčikovo-Nagymaros Project. Slovakia thus may be liable to pay compensation not only for its own wrongful conduct but also for that of Czechoslovakia, and it is entitled to be compensated for the damage sustained by Czechoslovakia as well as by itself as a result of the wrongful conduct of Hungary.
    153.
    Given the fact, however, that there have been intersecting wrongs by both Parties, the Court wishes to observe that the issue of compensation could satisfactorily be resolved in the framework of an overall settlement if each of the Parties were to renounce or cancel all financial claims and counter-claims.
    154.
    At the same time, the Court wishes to point out that the settlement of accounts for the construction of the works is different from the issue of compensation, and must be resolved in accordance with the 1977 Treaty and related instruments. If Hungary is to share in the operation and benefits of the Cunovo complex, it must pay a proportionate share of the building and running costs.
    155.
    For these reasons,

    The Court,

    (1) Having regard to Article 2, paragraph 1, of the Special Agreement,

    A. By fourteen votes to one,

    Finds that Hungary was not entitled to suspend and subsequently abandon, in 1989, the works on the Nagymaros Project and on the part of the Gabčikovo Project for which the Treaty of 16 September 1977 and related instruments attributed responsibility to it;

    in favour: President Schwebel; Vice-President Weeramantry; Judges Oda, Bedjaoui, Guillaume, Ranjeva, Shi, Fleischhauer, Koroma, Vereshchetin, Parra-Aranguren, Kooijmans, Rezek; Judge ad hoc Skubiszewski ;

    against: Judge Herczegh;

    B. By nine votes to six,

    Finds that Czechoslovakia was entitled to proceed, in November 1991, to the "provisional solution" as described in the terms of the Special Agreement;

    in favour: Vice-President Weeramantry; Judges Oda, Guillaume, Shi, Koroma, Vereshchetin, Parra-Aranguren, Kooijmans; Judge ad hoc Skubiszewski ;

    against: President Schwebel; Judges Bedjaoui, Ranjeva, Herczegh, Fleischhauer, Rezek;

    C. By ten votes to five,

    Finds that Czechoslovakia was not entitled to put into operation, from October 1992, this "provisional solution";

    in favour: President Schwebel; Vice-President Weeramantry; Judges Bedjaoui, Guillaume, Ranjeva, Herczegh, Shi, Fleischhauer, Kooijmans, Rezek;

    against: Judges Oda, Koroma, Vereshchetin, Parra-Aranguren; Judge ad hoc Skubiszewski;

    D. By eleven votes to four,

    Finds that the notification, on 19 May 1992, of the termination of the Treaty of 16 September 1977 and related instruments by Hungary did not have the legal effect of terminating them;

    in favour: Vice-President Weeramantry; Judges Oda, Bedjaoui, Guillaume, Ranjeva, Shi, Koroma, Vereshchetin, Parra-Aranguren, Kooijmans; Judge ad hoc Skubiszewski;

    against: President Schwebel; Judges Herczegh, Fleischhauer, Rezek;

    (2) Having regard to Article 2, paragraph 2, and Article 5 of the Special Agreement,

    A. By twelve votes to three,

    Finds that Slovakia, as successor to Czechoslovakia, became a party to the Treaty of 16 September 1977 as from 1 January 1993;

    in favour: President Schwebel; Vice-President Weeramantry; Judges Oda, Bedjaoui, Guillaume, Ranjeva, Shi, Koroma, Vereshchetin, Parra-Aranguren, Kooijmans: Judge ad hoc Skubiszewski;

    against: Judges Herczegh, Fleischhauer, Rezek;

    B. By thirteen votes to two,

    Finds that Hungary and Slovakia must negotiate in good faith in the light of the prevailing situation, and must take all necessary measures to ensure the achievement of the objectives of the Treaty of 16 September 1977, in accordance with such modalities as they may agree upon;

    in favour: President Schwebel; Vice-President Weeramantry; Judges Oda, Bedjaoui, Guillaume, Ranjeva, Shi, Koroma, Vereshchetin, Parra-Aranguren, Kooijmans, Rezek; Judge ad hoc Skubiszewski;

    against: Judges Herczegh, Fleischhauer;

    C. By thirteen votes to two,

    Finds that, unless the Parties otherwise agree, a joint operational régime must be established in accordance with the Treaty of 16 September 1977;

    in favour: President Schwebel; Vice-President Weeramantry; Judges Oda, Bedjaoui, Guillaume, Ranjeva, Shi, Koroma, Vereshchetin, Parra-Aranguren, Kooijmans, Rezek; Judge ad hoc Skubiszewski;

    against: Judges Herczegh, Fleischhauer;

    D. By twelve votes to three,

    Finds that, unless the Parties otherwise agree, Hungary shall compensate Slovakia for the damage sustained by Czechoslovakia and by Slovakia on account of the suspension and abandonment by Hungary of works for which it was responsible; and Slovakia shall compensate Hungary for the damage it has sustained on account of the putting into operation of the "provisional solution" by Czechoslovakia and its maintenance in service by Slovakia;

    in favour: President Schwebel; Vice-President Weeramantry; Judges Bedjaoui, Guillaume, Ranjeva, Herczegh, Shi, Fleischhauer, Parra-Aranguren, Kooijmans, Rezek; Judge ad hoc Skubiszewski;

    against: Judges Oda, Koroma, Vereshchetin;

    E. By thirteen votes to two,

    Finds that the settlement of accounts for the construction and operation of the works must be effected in accordance with the relevant provisions of the Treaty of 16 September 1977 and related instruments, taking due account of such measures as will have been taken by the Parties in application of points 2 B and 2 C of the present operative paragraph.

    in favour: President Schwebel; Vice-President Weeramantry; Judges Oda, Bedjaoui, Guillaume, Ranjeva, Shi, Koroma, Vereshchetin, Parra-Aranguren, Kooijmans, Rezek; Judge ad hoc Skubiszewski;

    against: Judges Herczegh, Fleischhauer.

    Done in English and in French, the English text being authoritative, at the Peace Palace, The Hague, this twenty-fifth day of September, one thousand nine hundred and ninety-seven, in three copies, one of which will be placed in the archives of the Court and the others transmitted to the Government of the Republic of Hungary and the Government of the Slovak Republic, respectively.

    President Schwebel and Judge Rezek append declarations to the Judgment of the Court.

    Vice-President Weeramantry and Judges Bedjaoui and Koroma append separate opinions to the Judgment of the Court.

    Judges Oda, Ranjeva, Herczegh, Fleischhauer, Vereshchetin and Parra-Aranguren and Judge ad hoc Skubiszewski append dissenting opinions to the Judgment of the Court.

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