ICSE Class 9 Answered

The process of depletion of oxygen in water bodies due to the disposal of organic and inorganic wastes in them is known as eutrophication.

When sewage, industrial effluents and fertilisers are discharged into rivers, many chemicals and nutrients are formed. These nutrients then get accumulated in the water resulting in the growth of phytoplanktons and algae. Their growth reduces the penetration of oxygen, light and heat into the water bodies. This threatens the lives of various marine organisms.