Eutrophication is a condition in a water body where high concentrations of nutrients
(such as nitrogen) stimulate blooms of algae, which in turn can cause fish kills and loss
of plant and animal diversity. Although eutrophication is a natural process in the aging of
lakes and some estuaries, human activities can greatly accelerate eutrophication by
increasing the rate at which nutrients enter aquatic ecosystems. Air emissions of
nitrogen oxides from power plants, cars, trucks, and other sources contribute to the
amount of nitrogen entering aquatic ecosystems.