Thermal pollution is the discharge of heated water into bodies of water. The main contributors to thermal heat pollution are thermal or nuclear power plants; industrial effluents such as petroleum refineries, pulp and paper mills, chemical plants, steel mills and smelters; sewage effluents; and biochemical activity. The ambient water temperature is the most vital requirements for survival of aquatic fauna and flora. The effects of thermal pollution include decrease the amount of dissolved oxygen in the water, which aquatic life requires, damage to larvae and eggs of fish in rivers, killing off some species of fish and macroinvertebrates that have a limited tolerance for temperature change, and migration of living entities from their environment.