StreamWatch BATS monitors the populations of organisms called macroinvertebrates at 14 sites. Water quality ratings are based on the abundance of various species and their sensitivity to pollutants. If the stream is healthy, a diverse macroinvertebrate population can be found in a relatively small sample of water. A reduction in their numbers may indicate a high level of pollution.
Sampling is conducted three times a year in March, July, and October, and the organisms are identified to family level in the Watershed Lab. Beginning in 2017, one sample per year will be sent to a certified lab for identification to the genus level.