Which of the following statements provides the best analysis of what happens to freshwater lakes that are polluted by nitrates and phosphates?
a.
nitrates and phosphates are lethal to fish populations.
b.
nitrates and phosphates promote algae bloom, increasing bacteria in the water, which use oxygen needed by marine life.
c.
nitrates and phosphates increase the acidity of the water, promoting the growth of some fish populations and the decrease of others.
d.
nitrates and phosphates have no effect on the fish population, but they limit plant growth by filtering the light they require to thrive.

The correct answer is - B. Nitrates and phosphates promote algae bloom, increasing bacteria in the water, which use oxygen needed by marine life.

The nitrates and phosphates when increased significantly in a water body is becoming very dangerous for the marine life. With the increase in nitrates and phosphates, the water is experiencing eutrophication. The algae thrive in those conditions and quickly spread out, and become the dominant in the water body. Because of the increase of algae, the water body starts to lose its oxygen, as also the light in the water body is much lower. The lack of oxygen and light results in the dying out of the marine life in the water body.