Eutrophication is the process by which minerals and nutrients, particularly nitrogen compounds and phosphorus compounds, accumulate in an entire body of water, or parts of it. In fresh water ecosystems it is nearly always the result of excess phosphorus compounds, whereas in marine ecosystems it is caused by either or both nitrogen and phosphorus compounds.
Eutrophication is a natural and very slow process in which nutrients enter from the degradation and solution of minerals in rocks and from the effect of lichens, mosses and fungi that actively absorb nutrients from rocks. Human-caused eutrophication is a much more rapid process in which nutrients are from any of a wide variety of sources, including untreated or partially treated sewage, industrial wastewater and fertilizer from farming, golf courses, lawns, etc.
Eutrophication often results in highly visible algal blooms, which are sometimes toxic to other organisms and which can also result in substantial habitat degradation by causing oxygen depletion after the bacterial degradation of the algae. This can lead to an invasion of alien species and an eventual reduction in biodiversity.
Eutrophication has become a major problem worldwide, with, for example roughly half of all lakes in North America, Europe and Asia now being eutrophic. The main technique for preventing and reversing it is reducing pollution from sewage, agriculture and other sources.