This empirical research analyzes the link between environmental agreements and the level of pollution in transnational waterbodies. It attempts to capture if environmental agreements have any impact on the actual level of pollution observed in transnational waterbodies and what are the determinants of the existence of such agreements. To answer these two questions, this paper matches the Global Environmental Monitoring System Water Database (which covers the period 1979-1990 and has the broadest coverage of waterbodies worldwide), with other variables such as the countries’ geographical locations, the existence of environmental agreements, the countries’ populations and their GDP’s. The econometric results indicate that the more specific the water treaties, the greater is their impact on water quality in international rivers. On the other side, a poor state of the water only seems to lead to signing of general treaties on frontier waters.