What is an overgrowth of aquatic plants followed by death decay and oxygen depletion?

An overgrowth of aquatic plants, often referred to as algal bloom, occurs when excess nutrients, particularly nitrogen and phosphorus, enter water bodies, leading to rapid plant proliferation. When these plants die and decay, the decomposition process consumes significant amounts of dissolved oxygen in the water. This depletion of oxygen can create hypoxic conditions, severely affecting aquatic life and potentially leading to fish kills and a decline in overall ecosystem health.