Roseau River Watershed Stressor Identification Report

The Minnesota Pollution Control Agency (MPCA) follows a watershed approach to systematically
monitor and assess surface water quality 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 2015 and 2016, the MPCA
conducted biological monitoring at several stations throughout the Roseau River Watershed (RRW). An
Index of Biological Integrity (IBI) score was calculated for each fish (F-IBI) and macroinvertebrate (M-IBI)
monitoring visit. The biological monitoring results for the RRW were then 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 four reaches were determined to have a
F-IBI and/or M-IBI impairment in the RRW, including segments of Hay Creek, Pine Creek, and Severson
Creek. This report identifies the probable causes, or “stressors”, that are likely contributing to the biological impairments in the RRW. Five candidate causes were examined as potential stressors for the biologically impaired reaches: loss of longitudinal connectivity, flow regime instability, insufficient physical habitat, high suspended sediment, and low dissolved oxygen (DO). Causal analysis was then performed to
determine and evaluate connections between each candidate cause and the biological impairments.