Answer:
Eutrophication
Step-by-step explanation:
Algal bloom:
Algal bloom is the overgrowth of algae in a marine or freshwater environment resulting in pungent odors and discoloration of water. Algal blooms arise in nutrient rich water due to a process called eutrophication.
Eutrophication is the presence of excess nutrients in water that promote the growth of algae and aquatic plants. This excessive growth results in the depletion of oxygen.
Eutrophication causes the build-up of inorganic chemicals such as ammonia, hydrogen sulphide and nitrites to a level that becomes toxic for fish and organisms. This coupled with depletion of oxygen kills fish resulting in the addition of more nutrients to the water.