The Guarani Aquifer System : from a beacon of hope to a question mark in the management/governance of transboundary aquifers

The Guarani Aquifer System is a transboundary aquifer shared by Argentina, Brazil, Paraguay and Uruguay. It stands as one of the largest reservoirs of freshwater worldwide and is one of the few transboundary aquifers whose management is regulated by an international treaty, the Guarani Aquifer Agreement. The latter is also the first to refer in its preamble to the UN International Law Commission Draft Articles on the Law of Transboundary Aquifers. This article traces the trajectory of transboundary cooperation over the past fifteen years over the Guarani Aquifer System. A first period (2002-2010) of positive cooperation in which the four countries actively moved forward towards a better understanding of the aquifer culminated with the adoption of the Guarani Aquifer Agreement in August 2010. A second period (2010-2017) has been marked by a slowdown in transboundary cooperation, limited in this period to sporadic cross border projects and initiatives linked to past and existing international projects. In this period only Argentina and Uruguay ratified the Guarani Aquifer Agreement. A third phase seems to be emerging in 2017 due to the possibility that finally Brazil and Paraguay ratify the Guarani Aquifer Agreement allowing it to enter into force. This article argues that in the future implementation of the agreement countries should build on the good practices, both substantive and institutional, stemming from the first period of transboundary cooperation