Little Sioux River Watershed Biotic Stressor Identification Report

The purpose of stressor identification is to explain the results of the biological monitoring and assessment process. The information obtained answers the questions of why one stream has a low index of biological integrity (IBI) score, while another has a high score. It looks at causal factors – negative ones harming fish and insects, and positive ones leading to healthy biology. Stressors may be physical, chemical, or biological. This report summarizes stressor identification work in the Little Sioux River Watershed. Located in southwest Minnesota, the Little Sioux River Watershed encompasses approximately 205,802 acres within the state of Minnesota. This watershed includes many large and small tributaries to the Little Sioux River. This report analyzed the biological impairments in two subwatersheds within the Little Sioux River Watershed. The subwatersheds having a biological impairment were: Little Sioux River Minor Watershed, and Ocheyedan River Minor Watershed. After examining many candidate causes for the biological impairments, the following stressors were identified for the impaired AUIDs in their respective subwatersheds (Table 1).