What is a key indicator of eutrophication in surface waters?

The presence of excessive algae growth is a key indicator of eutrophication in surface waters. Eutrophication occurs when water bodies receive an overload of nutrients, particularly nitrogen and phosphorus, often from agricultural runoff, sewage discharge, or other pollution sources. This nutrient enrichment stimulates the rapid growth of algae, leading to algal blooms.

These blooms can cover the surface of the water, blocking sunlight and disrupting the aquatic ecosystem. As the algae die and decompose, the decomposition process consumes oxygen, leading to hypoxic conditions, which can severely harm aquatic life, including fish and other organisms. This excessive algae growth is a visible sign that indicates poor water quality and an imbalance in the ecosystem, hallmark characteristics of eutrophication.