This Paper aims to examine the current legal regime of cross-border cooperation within the framework of the European Union and the Member States of the Council of Europe. In particular, this Paper analyzes the joint management of the international Guadiana River Basin by Spain and Portugal to assess whether it is necessary to link this cross-border cooperation definitively to the Council of Europe system and European Union law. According to this perspective, the management of the natural resources requires joint action along border territories, the consequence of which is the repurposing of the instruments for achieving such cooperation, and even rethinking the role of Public Law in the field of Cooperation. © 2020, Iustel. All rights reserved.