Eutrophication is a process by which plant growth increases in a lake or pond. In time, eutrophication may cause plants to completely fill in the area where a lake or pond once stood. The word "eutrophic" is of Greek origin, meaning "truly nourished."
The accelerated growth and overcrowding of plants is due to either natural fertilizing agents that are washed from the soil, or the runoff of chemical fertilizers applied to agricultural lands. Eutrophication may also be brought about by the drainage of sewage, industrial wastes, or detergents into a body of water.
As the overcrowded plants die off, the dead and decaying vegetation depletes the lake's oxygen supply. This, in turn, leads to the death of fish in the lake. The accumulated dead plant and animal material eventually changes a deep lake to a shallow one. The shallow lake then becomes a swamp, and finally it becomes dry land.
Sources: Cunningham, William P., et al. Environmental Encyclopedia, p. 205; Schneider, Herman. The Harper Dictionary of Science in Everyday Language, p. 113.