How do algae blooms indicate surface water quality issues?

Algae blooms are a direct indication of elevated nutrient levels, particularly phosphorus and nitrogen, in surface water bodies. When these nutrients are present in excess, often due to runoff from agricultural activities, wastewater discharge, or urbanization, they create ideal conditions for algae to grow rapidly. This phenomenon, known as eutrophication, can lead to the blooms that significantly alter the ecosystem.

As the algae multiply, they can cover the water's surface, blocking sunlight from reaching other aquatic plants and disrupting the balance of the ecosystem. When the algae die and decompose, this process depletes oxygen levels in the water, resulting in hypoxic or anoxic conditions, which are detrimental to fish and other aquatic animals. Therefore, the presence of algae blooms serves as a clear indicator of surface water quality issues, highlighting an imbalance caused by excessive nutrients leading to low oxygen levels in the water.