According to the U.S. Environmental Protection Agency, benthic macroinvertebrates, organisms that live on the bottom of streams and rivers, are prime indicators of localized environmental conditions because they: live in the water for all or most of their lives, stay in areas suitable for their survival, have limited mobility, often live no more than a year, and are integrators of their surrounding environment. Because they are susceptible to degradation of water, sediment, and habitat, their presence provides accurate information about the health of a stream and watershed.
Macroinvertebrates are sampled with a D-frame kick net that covers eight square feet are sampled per habitat site. The net is placed in the selected sampling location with the open end of the net facing upstream. A one-foot-square area of substrate in front of the net is disturbed and sampled for macroinvertebrates, which is then washed downstream into the net. Any large rocks, sticks, or other debris are removed from the samples before they are placed in containers and preserved with 95% ethanol.
Samples are sent to an independent laboratory for review and analysis. After removing any adult forms, non-aquatic organisms, and zooplankton, all other samples are enumerated and identified to the genus level. Chironomids are only keyed to family and non-insects are keyed to the order or family level. Up to 25 metrics are calculated for all samples from each site, metrics which include numbers of ephemeroptera, plecoptera, and trichoptera, percent dominance of three taxa, percent of sediment tolerant and intolerant species, percent shredders, the Hilsenhoff Biotic Index, and the B-IBI score.