Sauk River Watershed Stressor Identification Report

This report summarizes the key causes or "stressors", resulting in impaired fish and aquatic macro invertebrate communities of the Sauk River and its tributaries, a warm water river located in central Minnesota. The section of the Sauk River starting at Lake Osakis outlet downstream to the Horseshoe Chain of Lakes is listed on the 303(d) list of impaired waters for failing to meet established criteria for index of biological integrity (IBI). Stream biology is scored based on a numeric value given to a metric. Metrics are based on reproductive, feeding, or trophic characteristics that are specific to certain groups of fish and macroinvertebrates. Low scores indicate a lack of certain groups of fish and invertebrates which mean that the stream is not meeting expectations. The elements of a healthy stream consist of five main components; stream connections, hydrology, stream channel assessment, water chemistry, and stream biology. The following flowchart shows the five components of a healthy stream. If one or more of the components are unbalanced, the stream ecosystem fails to function properly and is listed as an impaired water body.