Water Quality Division

Assessment of Stream Aquatic Communities

Another important measure of aquatic ecosystem health is the status of its biological community. What type of organisms live there, how diverse is the community, and how healthy are the individual organisms are important indicators of the overall health of the system. OCC water quality specialists collect information on all stages of the food chain in streams beginning with the algal or periphyton (attached algae) community. OCC mainly concentrates on the density of the periphyton community, although sometimes we also consider what types or species of algae are dominant in the stream.

OCC also measures the type and densities of benthic macroinvertebrates (aquatic insects) that live in the stream. Certain species are indicators of poor or pristine water quality. In addition, whether or not the community is well balanced and diverse is a good indicator of pristine water quality. OCC follows Standard Operating Procedures (SOPs) based on EPA's Rapid Bioassessment Protocols (RBP) to collect and analyze this data. Benthic macroinvertebrate collections are usually made twice a year.

It is also important to consider the type and health of fish that live in a stream. Certain fish are more or less tolerant of pollution than others. In addition, the presence of lesions or tumors on a percentage of the population may suggest impacts of pollution in a stream. OCC collects fish at least once a year at each monitoring site.

Stream aquatic communities are assessed in conjunction with stream habitat and stream water quality to determine the stream's overall health.