A term derived from Greek words meaning "to nourish well" and referring to increased levels of nutrients in a lake or other body of water.

Lakes age naturally, becoming filled with plants and silt, forming marshes and finally, solid land.  This aging process (from a young or oligotrophic state to a mature or eutrophic state) normally takes thousands of years, but man's activities can speed up the process by increasing the supply of nutrients entering the lake.  These nutrients include phosphorus, nitrogen, carbon, potassium, trace elements, and vitamins.  Sources include human, animal and industrial wastes, agricultural and urban runoff, soil erosion, and even a sizable amount transported by the air.  Increases in nutrients cause rising rates of productivity, chiefly in the form of explosive growths or "blooms" of algae.  Decay of the algae can result in decreased oxygen levels in the deeper, colder layers of large lakes, killing fish. Steps which can be taken to reverse the eutrophication process involve reducing the level of nutrients entering water bodies through treatment of wastewater and reduction of runoff.