Q.Dissolved oxygen in water is responsible for aquatic life. What processes are responsible for the reduction in dissolved oxygen in water?

Water pollution results from human beings discharging waste — domestic sewage, industrial effluent, agricultural runoff — into ponds, lakes, streams, rivers, estuaries and oceans, on the mistaken assumption that flowing water simply carries pollutants away harmlessly. In India, the Water (Prevention and Control of Pollution) Act, 1974, was enacted specifically to protect water resources from this kind of contamination.

Water pollution takes several distinct forms covered as related concepts: domestic sewage discharge, which depletes dissolved oxygen and can spread disease; industrial effluents, which frequently carry toxic heavy metals and organic compounds that undergo biomagnification up the food chain; nutrient-driven problems such as eutrophication and algal blooms; and thermal pollution from heated wastewater discharged by power plants, which eliminates temperature-sensitive species. Addressing water pollution requires both regulation (legislation, monitoring of parameters like Biochemical Oxygen Demand) and treatment infrastructure, ranging from conventional sewage treatment plants to integrated, nature-based systems that combine engineered treatment with natural marshland filtration.