The objective of this paper is to evaluate the application of aquatic habitat variables to water quality objectives under authority of the Clean Water Act (CWA). The project is limited to freshwater, lotic aquatic habitats in the Pacific Northwest and Alaska with an emphasis on salmonid habitat. Habitat variables were placed into one of the following categories - flow regime, habitat space, channel structure, substrate quality, streambank condition, riparian condition, temperature regime, and habitat access. Candidate habitat variables were evaluated for their relevance to the biotic community, responsiveness to human impacts, applications to target landscapes, and measurement reliability. The most critical obstacles for use of habitat variables at the regional level (state specific water quality criteria for Region 10 EPA) are the quantification of biological effect and the unreliability of the unreliability of the measurement system.

"EPA 910-R-99-014." "July 1999." Cover title. "This document was developed for the US Environmental Protection Agency, Region 10, Seattle Washington, with the Idaho Water Resources Institute, University of Idaho." Includes bibliographical references (pages 70-77).

Challenges in developing habitat quality indicators -- Effect of natural disturbance on stream conditions -- Salmonid habitat requirements and land use effects -- Alteration of salmonid habitats by land-use practices -- Landscape context for habitat indicators -- Derivation of habitat indicator variables and stream classification -- Approach to habitat quality indicators -- Evaluation of potential aquatic habitat indicators -- Streambank and riparian condition -- Water column chemistry, habitat access & watershed condition -- Use of physical habitat variables in monitoring -- Case study of precision of physical habitat variables -- Application to water quality standards.