When there is an increase in the temperature of water bodies by industrial processes or activity of thermal power stations it is referred to as thermal pollution. The heated water causes a lowering of dissolved oxygen (DO) level in the body of water. As the DO content decreases the demand of oxygen increases in the water body, creating anaerobic conditions thereby disrupting the ecological balance.

Causes/Sources of thermal pollution:

Industrial Effluents- Industries require cooling water for heat removal and cooling purposes. This heated water when discharged into the water system increases the temperature of water body.

Nuclear Power plants-Nuclear power plants emit large quantity of heat and traces of radioactive substances which increases the temperature of water bodies.

Coal- fired power plants- It is one of the major source of thermal pollution.

Domestic sewage-When the domestic sewage is disposed off into water bodies like river, lakes etc it increases the temperature of receiving water.

Radioactive waste- Dumping of radioactive waste in marine system increases the temperature when these substances radiate energy.

Effects of Thermal pollution:

There are two types of effects of thermal pollution

Thermal shock: Due to decrease in DO levels there is suffocation of plants and animal species which creates anaerobic conditions .The sudden change in the temperature causes harm to the aquatic organisms.

Thermal enrichment:  The heated water is used for irrigation purposes to extend plant growing seasons. The warmer water also increases the metabolic rate of aquatic organisms (which in turn decreases the life expectancy of these organisms). The speedy growth is beneficial for commercial purposes.