Snake River Watershed Stressor Identification Report

The Minnesota Pollution Control Agency (MPCA) follows a watershed approach to systematically monitor and assess the quality of surface waters in each of the state’s 80 major watersheds. A key component of this approach is Intensive Watershed Monitoring (IWM), which includes biological (i.e., fish and macroinvertebrate) monitoring to evaluate overall stream health. In 2013 and 2014, the MPCA conducted biological monitoring at several stations throughout the Snake River Watershed (SRW). An Index of Biological Integrity (IBI) score was then calculated for the fish (FIBI) and macroinvertebrate (MIBI) communities of each station using the IWM and previously collected data. The biological monitoring results for the watershed were assessed to identify individual stream reaches that were not supporting a healthy fish and/or macroinvertebrate assemblage. A reach with a low IBI score(s) (i.e., below an established threshold) is considered “impaired” (i.e., unable to support its designated beneficial use) for aquatic life. A total of 11 reaches were determined to have an FIBI and/or MIBI impairment in the SRW, including segments of the Snake River, Middle River, South Branch of the Snake River, Judicial Ditch 28, and Judicial Ditch 29.