Thermal pollution is the degradation of
water quality by any process that changes ambient water
temperature. A common cause of thermal pollution is the use of water as a
coolant by
power plants and industrial manufacturers. When water used as a coolant is returned to the natural environment at a higher temperature, the change in temperature decreases
oxygen supply and affects
ecosystem composition. Fish and other organisms adapted to particular temperature range can be killed by an abrupt change in water temperature (either a rapid increase or decrease) known as "thermal shock."