Figure 1. Results of Rapid Bioassessment for Macroinvertebrates. Protocol II. Blue River of Southern Indiana. Y-axis represents percent similarity to pristine reference site, effectively splitting sites into nonimpaired, slightly, and moderately impaired stream habitats. We set an upper control limit of 79% to separate nonimpaired from slightly impaired, and a lower control limit of 54% to separate slightly impaired from moderately impaired.