In accordance with the FY 1991 Agency Operating Guidance , States and qualified Indian tribes are to adopt narrative biological criteria into State water quality standards during the FY 1991-1993 triennium. To support this effort, EPA is developing a Policy on the Use of Biological Assessments and Criteria in the Water Quality Program and providing this program guidance document on biological criteria. Like other water quality criteria, biological cri-teria identify water quality impairments, support regulatory controls that address water quality problems, and assess improvements in water quality from regulatory efforts. Biological criteria are numerical values or narrative expressions that describe the reference biological integrity of aquatic communities inhabiting waters of a given designated aquatic life use. They are developed through the direct measurement of aquatic community components inhabiting unimpaired surface waters.
Biological criteria complement current pro-grams.
Implementation of these programs has significantly improved water quality. However, as we learn more about aquatic ecosystems it is apparent that other sources of waterbody impairment exist. To effectively address our remaining water quality problems we need to develop more integrated and comprehensive evaluations. Biological criteria provide an essential third element for water quality management and serve as a natural progression in regulatory programs. Biological assessments have been used in biomonitoring programs by States for many years.