In a village in Karnataka, people started cultivating crops all around a lake which was always filled with water. They added fertilisers to their field in order to enhance the yield. Soon they discovered that the water body was completely covered with green floating plants and fishes started dying in large numbers. Analyse the situation and give reasons for excessive growth of plants and death of fish in the lake.
Because of the excessive use of fertilisers in the fields, they were carried down to the lake during rains. The fertilisers contain phosphates and nitrates, resulting excessive growth of algae and other aquatic plants which float on water surface. The submerged plants are killed due to shading and insufficient availability of dissolved oxygen resulted in the death of fish.