Thermal pollution primarily arises from waste energy generated from power plants, although it also comes from shoreline erosion, deforestation and runoff from paved surfaces. Thermal pollution refers to an artificial change in temperature, generally an increase from the average, in water bodies such as lakes, rivers, oceans and streams. This change in temperature stems from human activities such as the burning of coal and other fossil fuels and release of toxic byproducts into surrounding waters.
Thermal pollution classifies as a type of water pollution. Its severity and effect on surrounding habitats varies depending on the level of pollution and cause. Areas in the vicinity of power plants generally experience the greatest impacts from thermal pollution. Many power plants, particularly nuclear, gas and electric plants, require large amounts of water for cooling. Water cycles through the plants, then discharges at a warmer temperature into the surrounding waters. To a lesser extent, thermal pollution occurs through stream shading, a byproduct of erosion and deforestation.
Regardless of direct cause, thermal pollution produces significant effects on ecosystems. Sometimes, in the case of thermal shock, the warmer water temperatures resulting from this pollution harm plants and animals, killing organisms and reducing biodiversity. Some thermal pollution, called thermal enrichment, facilitates the growth of certain plants and animals.