Explanation

Eutrophication is increase in amount of nutrients in water due to detergents, pesticides, etc, and it leads to organic loading, depletion $of\ O_{2},$ etc. Eutrophicated lake (polluted water) has higher Biochemical Oxygen Demand (BOD), it is the amount of $O_{2}$in mg required to decompose organic matter present in one litre of heavily polluted water.