International Waters learning Exchange & Resource Network

Guaraní Aquifer System

The Guaraní Aquifer System extends from the central-west region of Brazil into Paraguay and the southeastern and southern regions of Brazil, and into northeastern Argentina and central and western Uruguay…It has an estimated total surface area of approximately 1.2 million square kilometers (839,800 km2 in Brazil, 225,500 km2 in Argentina, 71,700 km2 in Paraguay, and 45,000 km2 in Uruguay). The portion within Brazil encompasses about two-thirds of the total areal extent of the System, and includes parts of eight Brazilian states. An estimated fifteen million people live within the aquifer’s area of surface influence.



There is to date no binding legal agreement specifically governing the use of the Guaraní Aquifer System (“GAS”), a transboundary aquifer shared by Argentina, Brazil, Paraguay and Uruguay. Furthermore, of the four countries, only Paraguay has signed the 1997 United Nations (“UN”) Convention on the Law of Non-Navigable Uses of International Watercourses (which has not yet entered into force).

However, there are non-binding arrangements relevant to the GAS in place. The GAS Project (otherwise known as the Project for Environmental Protection and Sustainable Development of the Guaraní Aquifer System) was an undertaking by the four countries sharing the resource, the Global Environment Facility (“GEF”), the World Bank, and the Organization of American States (“OAS”). It developed a Declaration of Basic Principles and Action Guidelines, which declared that the Guaraní Aquifer, as a transboundary shared water resource, should be protected from contamination and sustainably managed. At the same time, the countries were called upon to use the aquifer in a manner that did not prejudice the environment or areas outside their territories, to maintain and share technical information, and to generally act in accordance with applicable principles of international law and the relevant international agreements to which they are parties.

In January 2009, the GAS Project issued its Strategic Action Program (“SAP”), which is intended to serve as a short and long-term planning instrument for Argentina, Brazil, Paraguay and Uruguay in regards to the GAS. The purpose of the SAP is to promote coordinated and sustainable groundwater management, while also respecting the countries’ national sovereignty over the aquifer. In addition, as part of the SAP, the GAS countries stated that would use the La Plata River Basin Treaty as the legal basis for actions relating to the GAS.


The countries that share the aquifer and participate in the SAP are Argentina, Brazil, Paraguay, and Uruguay. Those countries are also members of MERCOSUR – the Southern Common Market.


The Guaraní Aquifer System, named after the Guaraní Indigenous Nation, is one of the largest groundwater reservoirs in the world. The GAS was previously known as the Botucatu Aquifer in Brazil, the Tacuarembó Aquifer in Uruguay and Argentina, and the Misiones Aquifer in Paraguay. According to the World Bank:

The Guaraní Aquifer System extends from the central-west region of Brazil into Paraguay and the southeastern and southern regions of Brazil, and into northeastern Argentina and central and western Uruguay…It has an estimated total surface area of approximately 1.2 million square kilometers (839,800 km2 in Brazil, 225,500 km2 in Argentina, 71,700 km2 in Paraguay, and 45,000 km2 in Uruguay). The portion within Brazil encompasses about two-thirds of the total areal extent of the System, and includes parts of eight Brazilian states—an area equal to that of England, France and Spain combined. An estimated fifteen million people live within the aquifer’s area of surface influence.


The General Secretariat of the GAS Project is located in Montevideo, Uruguay. To support the implementation of the SAP, a GAS Liason Unit was established in Uruguay. The SAP does not refer to legal personality.


The GAS Project’s seven components included:

  1. Expansion and consolidation of the scientific and technical knowledge base regarding the GAS. According to the World Bank, the purpose was to develop a “sound scientific and technical basis for the determination of the priority transboundary issues and associated strategic remedial actions for the protection of the [GAS].”
  2. Joint development and implementation of a GAS Management Framework. This component was considered the “core” of the project, responsible for providing an “agreed technical, institutional, financial, and legal framework for the management” of the GAS, including “(i) harmonization and enhancement of data gathering networks, (ii) creation of a data management system serving the [GAS], (iii) development of joint institutional arrangements for the management of the [GAS], and (iv) formulation of strategic actions leading to the integration and optimization of development initiatives and proposals within the [GAS] region.”
  3. Enhancement of public and stakeholder participation, communication and education. This component provided for “the practical involvement of stakeholders in decision-making affecting the [GAS] through both formal and informal educational and informational programming.” The project also had a Guaraní Aquifer System Citizens’ Fund to provide cost-sharing funding to non-governmental organizations (“NGOs”) and academic institutions.
  4. Evaluation and monitoring of the project and dissemination of project results. This component involved the tracking of agreed indicators, including the GEF – International Waters (“GEF-IW”) process, stress reduction, and environmental status indicators, and the implementation of a monitoring and evaluation system to oversee and evaluate the Project’s progress and to disseminate the Project results.
  5. Development of regionally-appropriate groundwater management and mitigation measures in identified critical areas. The objective of this component was to develop practical mechanisms and mitigation measures in response to problems in certain hot spots and “to develop and test effective means and costs of quantifying, analyzing, managing, and remediating the impacts of known threats” affecting specific areas in the GAS.
  6. Assessment of geothermal energy potential. The objective of this component was to “quantify and determine the potential value of the [GAS] as a source of ‘clean’ geothermal energy and to communicate this assessment and appropriate guidelines” to stakeholders, including the energy ministries of the participating countries.
  7. Project coordination and management. This component included activities to be carried out by the GAS General Secretariat and “the operational activities of the coordinating and executing units” in the participating countries. For more information, see Organizational Structure.

In regards to the SAP, its general objective is “to consolidate the process of coordinated and sustainable groundwater management for the [GAS] in each of the participating countries, based upon the original [GAS Project]”. The countries, at both the national and regional levels, are supposed to pursue a coherent set of strategic actions to accomplish this objective, and to take such actions as needed to confront current and potential problems facing the GAS. And while focused on improving cooperation and coordination between the countries, the SAP also reaffirmed that resource management is a sovereign responsibility. In addition, the SAP promotes the exchange of information and the sharing of successful groundwater-management experiences.


i) GAS Project

The Project Steering Committee (“PSC”) was the highest-level decision-making body for the GAS Project’s execution phase. The PSC consisted of three representatives (from the national agencies responsible for foreign affairs, water resources, and the environment) from each GAS country, who served as National Coordinators. The PSC met at least twice a year. Representatives from the World Bank, the OAS, the GEF implementing agencies, and donor countries and agencies could be invited to attend the meetings of the PSC. A Coordination Group (“CG”), consisting of a National Technical Coordinator from each country, was responsible for overseeing the technical part of the GAS Project, as well as providing guidance to the General Secretariat and the Project Coordinator. The National Technical Coordinators headed the countries’ National Project Executing Units (“NPEU”).

The General Secretariat served as liaison between the NPEUs and the OAS and the World Bank, and managed the day-to-day operations of the GAS Project. The General Secretariat was headed by a Project Coordinator. The General Secretariat was responsible for overseeing the technical quality of the GAS Project; preparing documents and reports; supporting the World Bank’s monitoring, evaluation and reporting; drafting a Transboundary Diagnostic Analysis and the SAP; promoting the exchange of information, including inputs from stakeholders; publicizing the concerns of indigenous peoples and other community groups; and participating in regional coordination opportunities with other programs being executed in the region.

The OAS was the Executing Agency for the GAS Project. In addition to the OAS, there were the NPEUs in each of the countries, which were headed by the National Technical Coordinators. The NPEUs were responsible for overseeing project execution, providing oversight over the Project’s tasks, promoting the exchange of information, and encouraging inputs from stakeholders (especially in regards to indigenous people and other community groups). The following agencies in each country functioned as local executing agencies: Argentina – Subsecreteriat for Water Resources; Brazil – National Water Agency; Paraguay – Secretariat for the Environment; and Uruguay – National Directorate for Hydrography.

ii) The SAP

The SAP calls for a Regional Cooperation Council (“RCC”) to be created. The RCC, similarly to the PSC, consists of representatives from the ministries representing foreign affairs, national water resources, and environmental management in the four GAS countries. The NPEUs would become National Management Units and serve as inter-institutional bodies focused on water resources management. Technical Committees were institutionalized and are intended to provide support regarding the development of management instruments during the implementation of the SAP. In addition, the SAP calls for additional committees to be established – the Information System Committee (under the responsibility of Argentina), the Monitoring and Modeling Committee (under the responsibility of Brazil), the Capacity Building and Dissemination Committee (under the responsibility of Paraguay), and the Group for Promotion of Local Management (under the responsibility of Uruguay). In addition, the SAP made each country responsible for a Pilot Project. A GAS Liaison Unit, located in Montevideo, Uruguay, was also created to provide general support for SAP implementation, including disseminating information between the different committees and the decision-making and coordination bodies.


The GAS Project involved the four GAS countries, GEF, the World Bank, the OAS, and the International Atomic Energy Agency (“IAEA”). In formulating the SAP, in addition to Argentina, Brazil, Paraguay and Uruguay, the World Bank (as the Implementing Agency), GEF (for financial support), the OAS (as the Executing Agency), the IAEA (as a cooperating agency), and Germany’s Federal Institute for Geosciences and Natural Resources (BGR) (as a cooperating agency) were involved.

In addition, the GAS Project is dependent on international donor collaboration and funds to operate. See Funding and Financing.


The SAP calls on the countries to develop, by consensus, a coherent set of strategic actions in regards to the coordinated and sustainable groundwater management of the GAS.


The GEF Trust Fund Grant Agreement (see Funding and Financing) provided that any dispute arising out of, or related to, the Trust Fund Grant Agreement that could not otherwise be settled should be resolved by arbitration in accordance with the UNCITRAL Arbitration Rules.

The SAP does not provide specific details regarding dispute resolution among the four countries.


See Functions and Organizational Structure.


The GAS Project components included the evaluation and monitoring of the Project and dissemination of the Project results. See Functions.


The GAS Project’s budget was approximately US $26.7 million, of which approximately US $13.4 million was contributed by GEF and US $12.1 million by the four GAS countries. The IAEA, OAS, the Netherlands/World Bank Cooperation Project, and the German Geological Survey contributed, collectively, approximately US $1.2 million. According to the IAEA, its contribution to the Project was to assist the GAS Project in developing analytical techniques for isotope hydrology.

In July 2002, the World Bank and the OAS concluded the GEF Trust Fund Grant Agreement for the GAS Project, which stipulates the grant’s terms. Pursuant to this agreement, OAS entered into separate participation agreements with the four GAS countries. The participation agreements detailed each country’s role in the execution of the GAS Project. Part of the GEF Trust Fund Grant was used to establish a Guaraní Citizenship Fund, which was intended to support civil society activities in the GAS region (including promoting communication, public participation, and environmental education related to groundwater).

In addition, a grant from the World Bank and the Netherlands Water Partnership Program was used to establish the Guaraní Universities Fund, which provided financial support to regional universities and promoted capacity building activities in regards to the environmental and social aspects of the GAS.

In regards to the implementation of the SAP, US $180,000 was budgeted for the first stage of the implementation process, to be funded in equal amounts by Argentina and Brazil. Uruguay agreed to provide support for the GAS Liaison Unit.


No specific provision.


The GAS Project envisioned a “comprehensive Operational Monitoring and Evaluation System” to ensure supervision and assessment of outcomes, including the tracking of GEF-IW indicators. The monitoring systems were coordinated centrally within the General Secretariat, in coordination with the NPEUs who conducted monitoring at the local levels.

The GAS Monitoring Network is responsible for conducting certain quality and quantity measurements on 180 wells. According to the SAP, the GAS Monitoring Network should perform its work using existing national and local capabilities, and follow monitoring recommendations made by environmental control organizations and water supply companies. In addition, under the SAP, a Monitoring and Modeling Committee was established, consisting of academics and representatives of water resources institutions from each of the GAS countries. Brazil was charged with coordinating the committee. The main functions of the committee are: “to draw up an annual program of workshops and meetings; to negotiate with well-monitoring institutions and make data available to the GAS Monitoring Network; to provide technical support for selection of wells, sampling protocols and schedules.”


The World Bank has noted that national and sub-national governments of the participating countries, as well as “the population in the [GAS] region, local communities, NGOs, and academic institutions interested in sustainable groundwater use in the region—have been, and continue to be, involved in the project design and institutional arrangements for project implementation.” The GAS Project design provided for NGO, individual, private sector, and indigenous community involvement through the NPEUs. Also, a Guaraní Citizens’ Fund (see Functions and Funding and Financing) was established to support small projects implemented by NGOs (including community-based public education and awareness campaigns). Other project components, including expansion of the knowledge base, development of monitoring systems, and capacity-building, have involved the region’s academic community.

In response to the adoption of the SAP, meetings were held in the GAS countries, which included the participation of both public and private stakeholders, that focused on proposals and technical legal measures designed to increase the effectiveness of the GAS legal framework.

See also Functions and Organizational Structure.


The GAS Project officially ended in January 2009, with the issuance of the SAP. But, work continues under the SAP, which does not contain a termination date.





Agéncia Nacional de Aguas—Projeto Aqüifero Guaraní, available at (Portuguese only).

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