What is a common sign of high nutrient levels in aquatic environments?

The presence of thick algae growth is a prime indicator of high nutrient levels in aquatic environments, particularly nitrogen and phosphorus. When these nutrients are abundant, often due to runoff from agricultural activities or urban areas, they can cause algal blooms. These blooms can cover the surface of water bodies, blocking sunlight and disrupting aquatic ecosystems. This thick growth can lead to several ecological issues, including oxygen depletion when the algae die and decompose, which can harm fish and other aquatic organisms.

Clear water conditions, decreased insect diversity, and increased water temperature are not directly indicative of high nutrient levels. Clear water may occur with low nutrient inputs because there are fewer algae and sediments, while decreased insect diversity could be a result of various environmental stressors, including pesticide use or habitat destruction. Increased water temperature is influenced by factors such as climate, habitat structure, and exposure, rather than nutrient levels alone.