Question

why does the increased level of nutrients in the water affect the survival of aquatic organisms?

Answer 1

Availability of excess nutrients causes profuse growth of algae. Such algae may totally cover the water surface, often release toxins in water, and cause deficiency of oxygen in the water. Thus, in algae-infested water body the aquatic animals (e.g., fish) die due to toxicity or lack of oxygen. The process of nutrient enrichment of water and consequent loss of species diversity is called eutrophication.