Lake of the Woods 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. Between 2012 and 2014, the MPCA
conducted biological monitoring at several stations throughout the Lake of the Woods Watershed
(LOWW). An Index of Biological Integrity (IBI) score was then calculated for the fish (F‐IBI) and
macroinvertebrate (M‐IBI) 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 stream segment 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. Six reaches were determined to have an F‐IBI and/or M‐IBI impairment in the LOWW: Williams Creek, East Branch Warroad River, Willow Creek, West Branch Zippel Creek, Unnamed Ditch, and County Ditch 20.