ABSTRACT
A lake or a reservoir is intimately related with a watershed—a biogeophysical boundary—that is a drainage system connecting these natural or artificial bodies of water. A river basin or watershed is “defined as the entire area drained by a major river system and by its main tributaries” (Revenga et al. 1998). The watershed, thus, controls several mechanisms of functioning of lakes and reservoirs. Pristine watersheds not subjected to extensive modification by human activities contribute with low input of nutrients, suspended material, or toxic substances to the lakes and reservoirs. Degraded watersheds have a great impact on the functioning of the natural or artificial ecosystems that are connected to them. Figure 2.1 shows the main 106 watersheds of the world.
