Blue Earth River Watershed Stressor Identification Report

Over the past few years, the Minnesota Pollution Control Agency (MPCA) has substantially increased the use of biological monitoring and assessment as a means to determine and report the condition of the state's rivers and streams. This basic approach is to examine fish and aquatic macroinvertebrate communities and related habitat conditions at multiple sites throughout a major watershed. From these data, an Index of Biological Integrity (IBI) score can be developed, which provides a measure of overall community health. If biological impairments are found, stressors to the aquatic community must be identified. Stressor identification (SID) is a formal and rigorous process that identifies stressors causing biological impairment of aquatic ecosystems and provides a structure for organizing the scientific evidence supporting the conclusions (Cormier et al. 2000). In simpler terms, it is the process of identifying the major factors causing harm to aquatic life. SID is a key component of the major watershed restoration and protection projects being carried out under Minnesota's Clean Water Legacy Act. This report summarizes SID work in the Blue Earth River Watershed, along with the monitoring efforts within the assessment period. In total there were 69 stream reaches monitored for biology, roughly half failed to meet support for fish. Only five reached passed for fish assemblage at the highest threshold of the general use standard. Macroinvertebrate communities scored better overall, compared to fish. Out of 66 assessed sites, 43 of these sites passed for macroinvertebrate assemblage.