Data on species and their abundances be made understandable to the public and to water resource regulators while retaining the ecological information that is meaningful to biologists. A recent attempt to communicate such information is the Index of Biotic Integrity, or IBI (Karr 1981; Karr et al. 1986). The IBI is a means of quantifying ichthyologists' judgments of the relative quality of a fish assemblage. It is based on a sample of the entire fish assemblage, not just game fish. The index incorporates professional judgment of fish assemblage health in 12 metrics and their scoring criteria, which are based on regional ideals. These regional standards are determined from historical data and data from minimally affected sites that characterize the region. The individual metrics differ in their range of sensitivity for detecting perturbations, and a degree of redundance is built into the IBI because no single metric can reliably indicate integrity.