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Preliminary Reflections on the ICJ Decision in the Dispute between Chile and Bolivia Over the Status and Use of the Waters of the Silala

Friday, December 9th, 2022

The following essay, authored by Francesco Sindico, Laura Movilla Pateiro, and Gabriel Eckstein, was first published on EJIL: Talk!, the Blog of the European Journal of International Law. It is reposted here with their kind permission.


The Silala waters originate in Bolivia near its border with Chile, at an altitude of 4000 metres. This is one of the driest parts of the planet and home to unique mountain wetlands known as bofedales. In 1928, the Silala was heavily canalized on the Bolivian side of the border. According to Chile, this was done to address water quality concerns. Bolivia argued that the purpose was to enhance the quantity of Silala water flowing downstream.

A Silala canal in Bolivia

Chile and Bolivia, for the past six years, have engaged in a dispute before the International Court of Justice over the waters of the Silala. On 01 December 2022 the Court released its decision. This summary highlights some key facts and the outcome of the case, and raises a number of preliminary questions that the case presents about general international law and the law of international watercourses.

At the heart of the dispute is the “nature” and the “use” of the Silala. In a nutshell, Chile wanted the Court to “declare” the Silala an international watercourse entirely governed by customary international law, that its “use” was lawful according to international law, and that Bolivia’s recent proposals and efforts to use the Silala were unlawful. Bolivia presented counterclaims asking the Court to declare that it had sovereignty over both the infrastructure located in its territory and the enhanced portion of the surface flows, which benefitted Chile. Bolivia also sought a ruling that any future deliveries of enhanced flows to Chile had to be subject to an agreement.


Chile had always considered the Silala as an international watercourse. Bolivia started the proceedings considering the Silala to be domestic springs from which water was diverted downstream into Chile by means of the artificial infrastructure. Scientific studies commissioned by Bolivia during the judicial process revealed that the waters of the Silala would have flowed on the surface into Chile even without canalization. Thus, the positions of the two sides eventually converged. The only disagreement was on the effect of the infrastructure on the Silala’s surface flows with Chile maintaining that it was minimal (1 to 3%) and Bolivia considering that it was more significant (11 to 33%). Hence, Bolivia maintained that the Silala was an international watercourse with unique characteristics due to the extensive canalization infrastructure that enhanced the Silala’s surface flows. Bolivia, however, agreed in the oral proceedings that the Silala was subject to customary international law.

Silala Map
Map of the Silala Region

In deciding Chile’s first claim, the Court acknowledged that the parties had reached an agreement over the nature of the Silala as an international watercourse and that both agreed that customary international law applied to all of its waters. As a result, the Court concluded that the claim no longer had any object and that it did not have to issue a decision (§59).

The Court reached the same conclusion on Chile’s second (§65), third (§76) and fourth (§ 86) claims. In the second claim, it emphasized that both Parties agreed that the principle of equitable and reasonable utilisation applied to all the waters of the Silala, and that both parties were entitled to such utilisation. In the third claim, the Court highlighted statements made by both sides that Chile was entitled to its current use of Silala water as a function of its right to equitable and reasonable utilisation, and that such use was without prejudice to any future equitable and reasonable use that Bolivia might make, including related to the dismantling of the canals and restoration of the wetlands. With regard to Chile’s fourth claim—related to the threshold of harm that States must avoid when using the waters of an international watercourse in a way that causes pollution—the Court concluded that because Chile clarified its position during the proceedings that the actionable level was “significant” harm, as Bolivia had consistently argued, there was no disagreement between the Parties. In each of these claims, the Court acknowledged the agreement, ruled that it was devoid of any object, and declined to issue a decision.

Where the Court identified a disagreement in law and facts was in relation to Chile’s last claim. Here, Chile asserted that Bolivia had breached several procedural provisions of international law, namely the obligation to notify and consult with respect to measures that may have an adverse effect on other watercourse States. Since neither State is a party to the 1997 United Nations Watercourses Convention (UNWC) (§54), the Court decided the case on the basis of customary international law. However, Chile argued that Articles 11 and 12 of the UNWC reflected customary international law related to notification and consultation obligations. The Court rejected Chile’s assertion related to Article 11, clarifying for the first time in its case law that there was no state practice to justify such a conclusion (§111). It also acknowledged that while the Parties and the Court agreed that Article 12 reflected customary international law Chile and Bolivia had divergent views on the threshold that triggers a violation. According to Chile, “significant adverse effect” was the relevant threshold when considering application of the obligation to notify and consult on planned measures, as well as when the results of an environmental impact assessment must be shared. In contrast, Bolivia argued that the obligations only arise where there was a risk of significant transboundary harm. Relying on its jurisprudence in the cases of Certain Activities Carried Out by Nicaragua in the Border Area (Costa Rica v. Nicaragua) and the Construction of a Road in Costa Rica along the San Juan River (Nicaragua v. Costa Rica), the Court sided with Bolivia. While it acknowledged that the Commentaries to the Draft Articles on the Law of Non Navigational Uses of International Watercourses prepared by the UN International Law Commission did refer to the lower threshold, it concluded that Article 12 of the UNWC “does not reflect a rule of customary international law relating to international watercourses that is more rigorous than the general obligation to notify and consult contained in its own jurisprudence” (§117). The Court then reviewed the facts in the case and concluded that Chile had failed to allege or demonstrate any harm resulting from Bolivia’s planned measures on the Silala (§127). As a result, it unanimously rejected Chile’s claim (§128).

Bolivia’s three counterclaims received a similar fate as had Chile’s claims. The Court ruled that the Parties had reached an agreement during the proceeding on the first two, rendering them without object and negating the need for a decision; it also rejected Bolivia’s third claim.

Bolivia’s first counterclaim requested a declaration recognizing its sovereignty over the infrastructure and Bolivia’s right to remove it. In its second counterclaim, a corollary of the first, Bolivia requested a declaration of its sovereignty over the enhanced flow generated by the infrastructure. Since Chile had fully accepted Bolivia’s first counterclaim in its pleadings and during oral argument, the Court concluded that it was without object and required no decision (§147). Similarly, the Court considered that the Parties had reached a consensus on the second counterclaim as it related to Bolivia’s right to dismantle the canals and diminish the flow of the surface water downstream into Chile (§155). Thus, it also declined to rule on this point. As to Bolivia’s final counterclaim—asking the Court to declare that any need by Chile to have Bolivia maintain the infrastructure and enhanced flows would be subject to an agreement— the Court rejected it on grounds that it presented a hypothetical future scenario (§162).


The Silala case raises unique questions both for general international law and international water law. For the former, a key question relates to the consequence of new evidence and the Parties’ evolving positions during the proceedings that bring them closer to an agreement on the substance of a claim. In such cases, should the Court issue a declaratory judgement or, as occurred in the Silala case, is it free to declare a claim void of object that requires no decision? In this regard, see the Declaration of Judge Charlesworth and the Separate opinion of Judge ad hoc Simma. Another question pertains to the use of experts by the Parties, the Court’s request for cross-examination of the experts during the hearing, and the lack of nearly any reference to the science or experts in the decision.

From an international water law perspective, the Silala case appears to provide some clarification on the procedural obligation to notify and consult under customary international law. Question will surely be asked as to whether it has done so in a progressive or regressive manner. However, less clarity emerges from the decision on the extent to which riparians must cooperate to fulfil their obligations to notify and consult, on the nature of an international watercourse, and on the need to take into account the “uniqueness” of such a watercourse in the context of applying the principle of equitable and reasonable use.

While the Silala decision is distinct in being one of the few ICJ pronouncements on a dispute involving an international watercourse, it is still too early to comprehend is full value. In addition to the above, other questions will likely arise from the case for both general international law and international water law. For now, we hope these are enough to begin the discussion.

Francesco Sindico, Laura Movilla and Gabriel Eckstein all served as Counsel for the Plurinational State of Bolivia in the ICJ Silala case. None of what is written here should be attributed in any way to the Plurinational State of Bolivia, and only represents the positions and opinions of the three authors in their personal capacities.

Richard Paisley and Taylor Henshaw: The 1997 UN Watercourses Convention from a North American Perspective

Sunday, August 24th, 2014

The following post by Richard Paisley and Taylor Henshaw is the tenth and final essay in the series related to the entering into force of the 1997 UN Watercourses Convention (see links to all of the essays here). Messrs. Paisley and Henshaw are with the Global Transboundary International Waters Governance Initiative at the University of British Columbia in Vancouver, Canada, which Mr. Paisley directs. Mr. Paisley can be reached at: rpaisley [at]


The nations of North America—Canada, Mexico and the United States (USA)—share a significant number of international drainage basins and transboundary aquifers, comprising 16% of the world’s transboundary river basins. The three countries have entered into various bilateral agreements with their neighbors for the management and allocation of their transboundary waters. However, while each voted in favor of the UN Watercourses Convention (UNWC) when it came before the UN General Assembly, none of them has ratified the instrument. The objective of this essay is to critically consider the absence of these three nations from the roll of the UNWC and to assess whether ratifying and implementing the UNWC would be in the individual and collective best interest of all three countries.

International Freshwater Drainage Basins of North America. Source: UN Watercourses Convention Online Users Guide


The three nations appear to be in no great rush to ratify and implement the UNWC. This may be due to a perception that their international drainage basins are sufficiently managed without the UNWC: long-standing bilateral institutions have been established to deal with various aspects of the conservation and management of international drainage basins in North America.

Prominent among these mechanisms are the International Joint Commission (IJC) between Canada and the USA, and the International Boundary and Water Commission (IBWC) between Mexico and the USA. The history and practice of the IJC and the IBWC provide a rich body of work to review that falls beyond the scope of this essay. Nevertheless, it is pertinent to mention some of the challenges the two commissions face, such as: managing significant risks to water quality and quantity; the linking of border environments to binational trade and associated agreements; new stresses on public health and national economies; changes due to population growth and industrialization; greater demands on shared resources; increasing emphasis on public and indigenous peoples participation in decision-making; greater value placed on non-traditional water uses, such as “in stream” flows; and the imperative to establish ecosystem and active adaptive management approaches to resource management.

In addition, both institutions have experienced recent changes to their constituencies with the increasing influence of environmentalists and economic, social justice, and sustainable development advocates. As a result, ratification and implementation of the UNWC could help make both the IJC and the IBWC more relevant by increasing the focus on, and energy devoted to, the more sustainable conservation and management of transboundary waters and related resources in all three countries.

Substantive Objections

Whether and the extent to which Canada, Mexico and the USA have substantive objections to the UNWC is not well known. This may be because such objections are masked by the fact that all three countries were among, not just the 103 countries who voted in favor of the UNWC, but also the 38 countries to officially sponsor the UNWC.

On reflection, various substantive reasons may exist to explain why all three countries are not overly anxious to ratify and implement the UNWC. Mexico provides a good example. On the one hand, Mexico probably favors the UNWC, in part, because the Convention provides a basis for cooperating over measures to prevent, reduce and control pollution, including from the USA, which is an issue of great sensitivity to Mexicans. On the other hand, groundwater is tremendously important for Mexico where many believe that the conservation and management of shared transboundary aquifers necessitates a different international legal regime to that presented in the UNWC. More specifically, Mexico could be disinclined to ratify and implement the UNWC until more clarity is provided regarding the relationship between the UNWC and the emerging Draft Articles on the Law of Transboundary Aquifers. According to Stephen McCaffrey, such clarity, regrettably, may be a long way off and:

will crucially depend on eliminating both the overlap between the draft and the UN Convention in terms of the physical subject matter they regulate, and the notion of “sovereignty” over shared groundwater, which should have no place in any set of rules governing the use, protection, and management of shared freshwater resources.

Constitutional Politics

At the political level, the ratification and implementation of international treaties has become an increasingly challenging undertaking in all three countries.

In Canada, the negotiation, signing and ratification of international treaties is controlled by the executive branch of the federal government. However, many international treaties, such as the UNWC, deal with matters that fall under the provincial sphere of legislative jurisdiction pursuant to the division of powers in Canada between the federal government, the provincial governments and First Nations (sections 91, 92, 92A and 35 of the Canadian Constitution).  Also, according to Professor Emeritus of Economics and Forestry at the University of British Columbia, Peter Pearse:

A recurrent question in discussions about water management in Canada is “What is the role of the federal government?”  A stranger to these discussions might think, naively, that this is simply a constitutional question.  But even a good constitutional lawyer can not give a crisp answer.  To some extent the question is a political one – “What does the federal government think its role is, at the moment?”  This changes.

As a practical matter this means that ratification and implementation of the UNWC in Canada would likely trigger challenging and hard-nosed fiscal and other negotiations among the federal, provincial and First Nations levels of government. An analogous situation occurred when Canada was asked to ratify and implement the Espoo Convention on Environmental Impact Assessment in a Transboundary Context.

In the USA, the legal situation regarding international treaties is somewhat different, but possibly even more challenging. Under United States constitutional law, an international “treaty” is an agreement that has received the “advice and consent” of two-thirds of the United States Senate and has been ratified by the President (see here). As a practical matter, given the increasing political polarization within the United States Senate, obtaining the consent of two thirds of Senate members for any multilateral treaty, including the UNWC, would be exceedingly challenging.

Mexico is much closer to Canada constitutionally than to the USA as Mexico constitutionally allocates separate and exclusive spheres of authority to the states/provinces and the federal government. International treaties must conform to the Mexican Constitution in order to be valid. However, many international treaties address topics that in Mexico fall within the exclusive authority of the states/provinces. Seemingly, in practical terms this means that Mexico may need to enact domestic legislation to transform international treaty obligations into enforceable domestic law, which could be both time consuming and expensive.


Another reason why the UNWC has not yet been ratified and implemented in Canada, Mexico and the USA is the paucity of champions at the political level in all three countries. This resonates with Nicolo Machiavelli’s observation:

there is nothing more difficult to take in hand, more perilous to conduct, or more uncertain in its success, than to take the lead in the introduction of a new order of things. Because the innovator has for enemies all those who have done well under the old conditions, and lukewarm defenders in those who may do well under the new. This coolness arises partly from fear of the opponents, who have the laws on their side, and partly from the incredulity of men, who do not readily believe in new things until they have had a long experience of them.

Justifying the UNWC in North America

Despite the apparent obstacles noted above, there are at least three compelling reasons why Canada, Mexico and the USA should immediately ratify and implement the UNWC. First, ratification and implementation will send a strong and important message to each other, and to the world community, generally, that sovereign states have important rights and responsibilities when it comes to transboundary freshwater resources.

Second, the fact that Canada and the USA are variously both upstream and downstream of each other and that the USA is upstream of Mexico, will particularly and importantly help dispel any lingering misperception that the UNWC may be biased in favour of downstream or upstream states.

Third, Canadian, Mexican and American support for the Convention could not be more timely given how the world community is currently struggling with the harsh realities of climate change and water scarcity.

Ratifying and implementing the UNWC in North America would also demonstrate a wider acceptance of practice under the Convention as representing customary international law. In turn this could place the UNWC higher on various political agendas and could help lead to a more stable framework for transboundary water cooperation globally.