Citizen Science

Biological Indicators

A good way to understand the overall health of a stream is to monitor the aquatic life in it. Small aquatic organisms, also called benthic macro invertebrates, are excellent indicators because they cannot escape changes in water quality. These aquatic organisms include the aquatic insects, crayfish and other crustaceans, clams and mussels, snails, aquatic worms, and other similar organisms. Insects comprise the largest diversity of these animals and include mayflies, stoneflies, caddisflies, and midges. They cycle nutrients, and are major food sources for fish and other aquatic animals.

By determining the number and type of insects that live in a stream, the quality of the water and the health of the stream environment can be assessed. For example, stonefly nymphs are sensitive to most pollutants.

If habitat and chemical parameters are good, a stream will support insects sensitive to pollution, and the stream can be considered healthy. If a stream has many pollution tolerant insects, such as midges and black fly larva, or not much variety, then the biological assessment indicates that stream health is "poor."