WordNet
n. harm to lakes and rivers resulting from the release of excessive waste heat into them
Wikipedia
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."
Urban runoff— stormwater discharged to surface waters from roads and parking lots—can also be a source of elevated water temperatures.
Usage examples of "thermal pollution".
He trumpets the dangers to our rivers of raw sewage and industrial toxins and thermal pollution.
Although in that case the scanning team would have spotted something beyond a little thermal pollution, no?