What is a primary consequence of high nutrient levels in water bodies?

High nutrient levels in water bodies, commonly referred to as nutrient pollution, often lead to eutrophication, which is the over-enrichment of water with nutrients, primarily nitrogen and phosphorus. This process typically results in excessive growth of algae, or algal blooms, which can significantly reduce aquatic biodiversity.

As these algal blooms proliferate, they can block sunlight from reaching underwater vegetation, disrupting the growth of plants essential to aquatic ecosystems. Furthermore, when the algae die and decompose, a process that consumes oxygen occurs, leading to hypoxic (low oxygen) conditions. This deterioration of water quality can be detrimental to various aquatic species, especially those that require higher oxygen levels, resulting in declines in their populations and overall biodiversity in the ecosystem.

In contrast, the other choices relate to outcomes that generally do not occur as a direct result of high nutrient levels in water bodies. Increased fish populations would usually only occur under healthy conditions and in balance with nutrient levels, while high nutrient levels often lead to fish kills due to oxygen depletion. Reduced sediment accumulation is unlikely because increased plant and algal growth can lead to more sedimentation issues, and increased oxygen levels are generally not a consequence of nutrient over-enrichment.