Lower BOD of a water body helps reappearance of clean-water organisms. Explain.

Lowering of Biological Oxygen Demand (BOD) results in decreased biodegradable material in the water body → As result of which there is reduced microbial decomposition → when there is no decomposition oxygen utilisation reduced → more Dissolved Oxygen (DO) available (clean water-organisms reappear).

Lowering of Biological Oxygen Demand (BOD) results in decreased biodegradable material in the water body. This results in reduced microbial decomposition. When there is no decomposition, oxygen utilisation is reduced and there is more Dissolved Oxygen (DO) available. Thus, clean water-organisms reappear.