热污染是指人类活动造成水温的不正常上升。

工厂或发电厂使用水作为冷冻剂，用完后排出海洋或河流。虽然这些水未必含有害物质，并未造成水污染，但其高温却会影响水中的生态。

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."