Answer:
Nitrogen and phosphorus pollution which causes the increase in population of phytoplanktons lead to the process called euthrophication.
Step-by-step explanation:
Eutrophication occurs when there is excessive level of phosphorus and nitrogen in the water that leads to the increase in population of phytoplanktons or algal blooms. Algal blooms has a negative effect to the quality of water for it creates an environment suited for the growth of bacteria and thereby decreasing the supply of oxygen in water. This leads to death of fishes and aquatic life.