According to the official definition of the United States Environmental Protection Agency (EPA), bioassessment refers to the process of evaluating the biological condition of a body of water using biological surveys (biosurveys) and other direct measurements of the resident biota—those organisms living in the surface water, including fish, insects, algae, plants and others. Since 1972 when the Clean Water Act was passed by Congress in order to clean up America's polluted waterways, the biological integrity of the nation's bodies of water has been the focus of professionals and citizens in ensuring the success of reaching this goal.

The derivation of biocriteria emerges from the bioassessment, and offers a narrative or numeric expression that explains the life surviving in the water. The process of evaluating biocriteria can be in "scores" using a method known as the Ohio multimetric approach; or, reported in "clusters" according to the Maine statistical approach...