Power plants- thermal and nuclear, chemical and other industries use lot of water (about 30% of all abstracted water) for cooling purposes and the used hot water is discharged into rivers, streams or oceans. The waste heat from the boilers and heating processes increases the temperature of the cooling water. Discharge of hot water may increase the temperature of the receiving water by 10 to 15°C above the ambient water temperature. This is thermal pollution. Increase in water temperature decreases dissolved oxygen in water which adversely affects aquatic life. Unlike terrestrial ecosystems, the temperature of water bodies remain steady and does not change very much. Accordingly, aquatic organisms are adopted to a uniform steady temperature of environment and any fluctuation in water temperature severely affects aquatic plants and animals. Hence discharge of hot water from power plants adversely affects aquatic organisms. Aquatic plants and animals in the warm tropical water live dangerously close to their upper limit of temperature, particularly during the warm summer months. It requires only a slight deviation from this limit to cause a thermal stress to these organisms.

Discharge of hot water in water body affects feeding in fishes, increases their metabolism and affects their growth. Their swimming efficiently declines. Running away from predators or chasing prey becomes difficult. Their resistance to diseases and parasites decreases. Due to thermal pollution biological diversity is reduced. One of the best methods of reducing thermal pollution is to store the hot water in cooling ponds, allow the water to cool before releasing into any receiving water body.

Choose the factor which is NOT true about the below given statement:

Discharge of hot water in water bodies -

increases resistance to diseases

The correct answer is Option (2) → increases resistance to diseases

The factor that is NOT true about the given statement "Discharge of hot water in water bodies" is: Increases resistance to diseases

Explanation:
While the other statements are accurate in describing the impacts of hot water discharge on aquatic organisms, the statement about increasing resistance to diseases is not true. In fact, the increase in water temperature and the associated stress on aquatic organisms can often lead to a decrease in their resistance to diseases and parasites. The elevated temperature can weaken their immune systems, making them more susceptible to illnesses and infections. Therefore, the discharge of hot water can actually decrease the resistance of aquatic organisms to diseases.