Eutrophication of water bodies leading to killing of fishes is mainly due to non availability of Oxygen, Light, Food, Essential minerals

Lakes are eutrophied by sewage, agricultural and industrial wastes. The prime contaminants are nitrates and phosphates, which act as plant nutrients. They overstimulate the growth of algae, causing scum and unpleasant odours, and reduce the amount of dissolved oxygen vital to other aquatic life. At the same time, other pollutants flowing into a lake may poison whole populations of fish, whose decomposing remains further deplete the dissolved oxygen content. In such fashion, a lake can literally choke to death. Thus, the correct answer is option A.