What aspect of water quality does biological assessment primarily focus on?

Biological assessment focuses primarily on the organisms present in the water. This approach evaluates the health of aquatic ecosystems by studying the diversity and abundance of organisms, such as macroinvertebrates, fish, and algae, found in a particular water body. These organisms serve as indicators of the overall ecological condition, reflecting the impacts of various stressors like pollution, habitat alteration, and nutrient loading on water quality.

By examining the types and populations of organisms, biologists can assess the biological integrity of a water body. Healthy ecosystems are characterized by a diverse array of organisms, while declines in diversity or the presence of sensitive species often indicate problems caused by environmental stressors. Thus, biological assessments provide crucial insights that cannot be captured through purely chemical or physical measurements, helping to gauge the overall health of aquatic environments effectively.