Thermal pollution causing increase in average temperature.Large amount of water is used for cooling purpose in thermal and nuclear plants, industries, etc. The cooling water is discharged with an increased temperature, thus the average temperature of the water body increases and is known as thermal pollution.
As the temperature of water increases, the amount of dissolved oxygen decreases making aquatic life difficult. Aquatic life cannot survive in hot waters. The rate of chemical reaction increases with increase in temperature and therefore the rate of decomposition of organic matters also increases. The viscosity and density of water decreases which increase the rate of setting down of suspended particles. The rate of evaporation increases which leads to large amount of water loss.