Fishes in eutrophic lake die due to

Eutrophic lakes have high levels of biological productivity due to the rich nutrient constituents, especially nitrogen and phosphorus. An abundance of plants are supported in this lake. Initially, eutrophic lakes accelerate multiplication and growth of lake fauna. Plants and/ or algal blooms overcrowd the lake, they later die and decomposition of dead organic matter starts which leads to decrease in dissolved oxygen content. Decrease in dissolved oxygen suffocats lake fauna, e.g., fishes to death.