Answer:
Eutrophication can be defined the process by which the there is a significant increase in the population of algal growth.
This increase in the algal growth is due to the increase in the phosphorous and nitrogen in the water bodies.
The phosphorous increases the growth of algae in the nearby water bodies and depletes the oxygen level in water bodies.
So, Eutrophication is caused by excess of fertilizer(phosphorous) in water.