What is primarily affected by nutrient levels in water bodies?

The health of aquatic life is primarily affected by nutrient levels in water bodies because nutrients, particularly nitrogen and phosphorus, play a significant role in the growth and development of aquatic organisms. When nutrient levels are too high, it can lead to eutrophication, which causes excessive growth of algae. This algal bloom can deplete oxygen levels in the water and block sunlight, which harms fish and other aquatic species, disrupting the entire ecosystem.

Conversely, low nutrient levels can limit the growth and reproduction of aquatic plants and animals, leading to a less diverse and less healthy aquatic community. Thus, monitoring and managing nutrient levels are crucial for maintaining the overall health of ecosystems within water bodies. The other options, while relevant in certain contexts, do not directly relate to the impact of nutrient levels on the biological health of aquatic life.