Reservoirs are complex artificial ecosystems, oscillating with and responding to several impacts of climatological, hydrological and anthropogenic forcing functions. The functioning of the reservoirs, is thus related to the multiple impacts of climatological factors, to the interaction of climatology / hydrology with the natural functions of the watersheds and the reservoirs and to the multiple uses of the reservoirs. The impacts of multiple activities in the watersheds and reservoirs is well documented is many regions, and this is a background for management: predictive, integrated, adaptative and at the watershed level. In order to improve and enhance the multiple use of reservoirs an equilibrium of social and economic perspectives and innovative technological developments should be promoted. The integration of research, planning and management is a fundamental concern, in reservoir science and application. Since the forcing functions vary with latitude and multiple operational uses, the result is qualitative and quantitative differences in a reservoir or reservoir cascades. Therefore, several regional approaches to their management are required. Economic evaluation of the "services" provided by reservoirs should be performed in order to provide a realistic balance of the positive / negative impacts of their construction. Reservoirs in the Metropolitan Region of Silo Paulo represent special cases due to their strategic value in water supply and multiple uses.