The life in, and physical characteristics of, an aquatic system provide insight into the historical and current status of its quality. The assessment of an aquatic system based on the organisms living in it is called biomonitoring. The assessment of the system based on its physical characteristics is called a habitat assessment. Biomonitoring and habitat assessment are two tools that limnologists at the University Hygienic Laboratory use to assess the water quality for many stream projects. Biomonitoring is the process of inventorying aquatic organisms in a selected region of an aquatic system.
All organisms have a tolerance level for pollutants.
Tolerance levels vary from organism to organism. Thus, it is possible to determine at a point in time, qualitatively, the level of water quality impairment based on what fauna are present and their abundances. It is also possible to monitor changes in water quality by repeated sampling of the same areas over an extended period of time. Habitat assessment is the process of evaluating the physical characteristics of a stream. This is accomplished by quantifying parameters such as stream flow, depth, width, substrate type, bank stability and erosion potential, instream deposition and scour, and instream cover.