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 waterbody was completely covered with green floating plants and fish in the lake started dying in large numbers. Analyse the situation and give reasons for excessive growth of plants and death of fishes in the lake.

During rains, the fertilisers added to the fields ran off into the lake. Presence of high amount of phosphates and nitrates enriched the lake water with the same nutrients. Presence of these compounds promoted the growth of aquatic plants which covered the surface of the lake. This phenomenon is known as eutrophication. This blocked the water from sunlight and oxygen which resulted in the death of fish.

NOTE: Eutrophication is defined as the process by which a body of water becomes enriched in dissolved nutrients such as phosphates that stimulate the growth of aquatic plant life usually resulting in the depletion of dissolved oxygen.