The La Plata River Basin is one of the largest international river basin in the world, with an area of about 3.1 million km2. It includes parts of five countries (Argentina, Bolivia, Brazil, Paraguay and Uruguay) and its water resources are essential for their economic development. Together with reservoir development for hydropower, extensive deforestation, intensive agriculture practices and large urban development took place in the Parana, Paraguay and Uruguay basins affecting environmental conditions and raising important issues concerning water resources use and conservation which can be illustrated by the occurrence of blue green algae bloom, excessive sedimentation, and related water quality degradations. Therefore the need to promote participatory and cooperative efforts among water resources stakeholders as well as systematic interchange of information and experiences on common regional problems among organizations and experts throughout the basin devoted to water resources use and management, was claimed by researchers and managers gathered in the I and II International Workshops on Regional Approaches for Reservoir Development and Management in the La Plata River Basin held in 1991 and 1994, respectively. As a concrete response to said need, efforts carried out by a number of organizations from various countries within the Basin, with the support of international and national governmental organizations including Japanese Governmental and Non-Governmental Organization, succeeded in the foundation of La Plata River Basin Environmental Research and Management Network (RIGA), carried out in March 2001, within the framework of the III International Workshop, which was precisely one of the short term activities included in RIGA Action Plan.