Phosphorus plays a central role in the bioenergetics of organisms and ecosystems. It is a role which no other atom can duplicate. Phosphorus is of paramount importance in lake management because it most often limits the degree of phytoplanktonic autotrophy (algae growth).

A lake or reservoir ecosystem doesn’t stop at the shoreline: it includes all land which drains to it (the watershed). The quality of water entering a lake or reservoir from surrounding land has a direct effect on the quality of water in the lake or reservoir. The quality of water coming from a watershed depends on the activities taking place on the land. Lakes reflect the quality of their watersheds, they are mirrors of the landscape.