Many of the technical reports published by the Commission include scientific assessments of stream life communities. The Commission evaluates stream life as one means to qualitatively characterize stream conditions. Through 2014, the Commission used the U.S. Environmental Protection Agency's Rapid Bioassessment Protocol (RBP) (EPA/444/4-89-001) to assess stream communities. The RBP outcome assigns one of four Biological Condition Categories (e.g., nonimpaired, slightly impaired, moderately impaired, and severely impaired) that compare the assessed stream's living community traits with conditions of a similar reference stream.
State agencies that regulate water quality and determine the designated use of waters pursuant to the federal Clean Water Act (CWA) also use the terms "assessment" and "impaired." When applied in the context of CWA regulations, the terms "assessment" and "impaired" convey specific legal meaning. Because the Commission's assessments are not for regulatory purposes, our use of the term "impaired," consistent with RBP Biological Condition Categories, describes a qualitative comparison with a reference setting only. To avoid confusion over the term "impaired," in 2015, the Commission began using a different data analysis method that allows the application of descriptive characterizations of water quality at sites (e.g., very good, good, fair, poor, and very poor).
Technical Report (PDF) (48 pages, file size = 1.55MB)