The term for the accumulation of excessive nutrients in water bodies is eutrophication. This process typically occurs due to runoff from agricultural lands and urban areas, leading to high concentrations of nitrogen and phosphorus in aquatic systems. Eutrophication can result in algal blooms, which deplete oxygen levels in the water and harm aquatic life. The subsequent dead zones can disrupt entire ecosystems, impacting fish populations and biodiversity and causing shifts in species composition.