Water used for cooling by power plants and factories is commonly returned to its original source at a temperature greater than its original temperature. This heated warm water leaves an outlet pipe in a stream-like flow known as a thermal plume . The water within the plume is significantly warmer than the water immediately adjacent to it. Thermal plumes are environmentally important because the introduction of heated water into lakes or slow-moving rivers can have adverse effects on aquatic life. Warmer temperatures decrease the solubility of oxygen in water, thus lowering the amount of dissolved oxygen available to aquatic organisms. Warmer water also causes an increase in the respiration rates of these organisms, and they deplete the alreadyreduced supply of oxygen more quickly. Warmer water also makes aquatic organisms more susceptible to diseases, parasites , and toxic substances.
See also Thermal pollution