What phenomenon is characterized by excessive growth of algae due to nutrient pollution?

Eutrophication is a phenomenon that occurs when water bodies receive an excess of nutrients, particularly nitrogen and phosphorus, which often come from agricultural runoff, sewage, or other pollution sources. This influx of nutrients stimulates the rapid growth of algae, commonly referred to as algal blooms. These blooms can significantly alter the ecosystem, leading to problems such as reduced sunlight penetration in the water, which affects the growth of aquatic plants, and oxygen depletion as the algae die and decompose.

When the algae die, their decomposition consumes oxygen in the water, leading to hypoxic or anoxic conditions that can harm or kill fish and other aquatic life. This cycle underscores why eutrophication is a critical environmental issue, as it can create dead zones in water bodies where aquatic life can no longer survive. The other options relate to different processes: biomagnification refers to the increasing concentration of toxins in organisms at higher trophic levels; ocean acidification involves the decrease in pH levels of ocean waters due to increased carbon dioxide; and oxygen depletion specifically addresses the lack of oxygen, which can be a consequence of eutrophication.