Although the IFIM is used worldwide, a critical review of the origins of the habitat criteria concept has never been conducted to determine important assumptions, ensure proper use, and lay a scientific foundation for future development. We review the evolution of the habitat criteria concept to better understand how and why species criteria were first developed. The first use of habitat criteria in river habitat assessments began some time before 1965, expanded gradually in the 1970's, and became common in the late 1970's and 1980's. The concept originated in the northwest U.S. states of California, Washington and Oregon, and the province of British Columbia. Habitat criteria were used to link the biology of fish to the physical characteristics of a stream. Importantly, development of habitat criteria was usually coupled to water management decisions. Decision-makers needed to link fish biology, stream morphology and hydraulic patterns, and water management. The earliest institutional pressures to create the habitat criteria concept to support development of instream flow requirements came either in response to proposals to construct reservoirs with inadequate releases to support downstream aquatic resources or to reserve flows as a water right to sustain inland fisheries in the face of over appropriation of water rights. One of the objectives of the paper is to ask for help in locating information not know to the authors.
