The presence, condition and numbers of types of fish, insects, algae, plants, and other organisms provide important information about the health of aquatic ecosystems. Studying these factors as a way of evaluating the health of a body of water is called biological assessment. Biological criteria are a way of describing the qualities that must be present to support a desired condition in a waterbody and serve as the standard against which assessment results are compared.

• Technical Assistance Documents for States, Tribes and Territories
  This page contains links to general and waterbody specific guidance and technical documents for biological criteria and assessment programs.
• Program Overview
  This page provides an overview of the Biological Criteria and Bioassessment Program through a compilation of fact sheets, memos and programmatic information.
• Case Studies
  This page contains case studies on how bioassessment information and biological criteria have been used for a variety of water quality management activities such as development of ant-degradation policies, assessment, permitting, and enforcement.