Thermal pollution

While producing electricity, the combustion of fossil fuels produces heat energy, some of which is used to generate electricity. Because the process is not entirely efficient, much of the heat is released to the atmosphere or to water that is used as a coolant. Heated air is not a problem, but heated water, once returned to rivers, streams or lakes, can disturb the aquatic ecosystem. This is not a massive problem, as global warming and air pollution are, but as it is a problem, it cannot be entirely forgotten.