After nutrient enrichment from sewage contamination, a lake often becomes inhospitable to fish. Why?
Nutrient input to a lake causes the explosive growth of algal and cyanobacterial populations. This reduces the penetration of light into the lake, the water temperature falls, and eventually the fish population dies.
Nutrient input to a lake poisons the fish.
Nutrient input to a lake poisons the organisms that fish eat.
Nutrient input causes the death of algae and cyanobacteria and, thus, the ultimate sources of organic compounds in a lake ecosystem. Eventually, this reduces the availability of food for fish within the lake, leading to their death.
Nutrient input to a lake causes the explosive growth of algal and cyanobacterial populations. Decomposition of dead algae and cyanobacteria by bacteria results in the depletion of oxygen in the water, which leads to the death of fish.