Power plants use water for cooling. The quantity of water required by any fossil fuel fired power plant is huge - up to a billion gallons each day! As this water is discharged back to the river, thermal (heat) pollution occurs. This huge quantity of warmer water can create ice-free pockets in winter of cold countries, which can attract and then trap many species when the flow slows or stops. In summer, the hot water can add to oxygen-deficiency in the river water, choking fish and aquatic life. Heavy metals and chlorine in cooling water discharges are also having a negative effect on aquatic life in rivers and other water bodies.
Rivers which act as estuarine type nursery of ocean fish species are badly affected by such polluted water from power plants. There are millions of tiny fish eggs, larvae, and very young fish essentially adrift in the water, and hence extremely vulnerable to power plant cooling water intakes. These small animals are often killed by the passage through a plant’s cooling system. In some cases, about 60% mortality of newborn fish stock have been reported due to power plants. Moreover, Adult fish are also trapped and pinned to intake screens by the force of the suction.