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human needs, to provide and protect the instream flows and habitat needed to maintain and recover the endangered fishes, [and] to protect other native fish and wildlife resources in the Yampa River Basin." As required by law, this project will conform to the requirements of the NEP A process. As a part of the NEP A process, the following study was initiated to address concerns related to low flow needs of the endangered fishes in the Yampa River. Our approach was to define the relationship of habitat availability to reduced flows and relate habitat use by fishes to that relationship. Flow/habitat/fish relationship studies have several components. We defined habitat types by characteristics, such as depth, velocity and substrate. Habitat preference, which we define as the ratio of a habitat used to the total usable habitat, for a species of interest needs to be determined. And then the availability of quality habitats needs to be measured and quantified as a function of flow. As flow declines, quality/preferred habitat may also decline and eventually become lost or dispersed. When conditions do not allow large fish to move across shallow riffles, they become isolated in whatever habitats remain. The rate of habitat loss or habitat isolation due to flow reductions (flow/habitat relationship) can be accurately predicted using hydraulic simulation models. However, the relationship between habitat availability and fish survivability is much more difficult to predict precisely because of variations in local channel morphology, stream productivity, and an individual fishes' ability to adapt to adverse flow conditions. Therefore interpretation and conclusions concerning impacts of habitat loss or habitat isolation are dependent on familiarity with and knowledge of the quality and quantity of information on life history and habitat needs not only of a species, but of the aquatic community. The goal of this study is to determine habitat availability at various low flow scenarios and habitat use patterns of endangered fishes in the Yampa River during the lowest flow period of the year (i.e. August - October). The specific objectives of this study include: 1) determine the composition, dimensions and characteristics of riverine habitat at randomly selected sites in the Yampa River at low flows during the 1996-1997 baseflow period, 2) Monitor the movements of Colorado squawfish, humpback chub, northern pike, and channel catfish in the Yampa River during the low flow periods to determine the range of movement and habitats occupied (CS and HC) during the baseflow periods, and postmigrational movement (CS) through Cross Mountain Canyon. 3) Using the data collected on habitat availability (including the depth at which riffles become barriers to movement) and fish movement during the baseflow periods of two years, develop a recommendation on the need for low flow management in the Yampa River. The study has three major components: 1) Radio telemetry: to determine habitat use and movement behavior of adult Colorado squawfish, humpback chub, northern pike Esox lucius and channel catfish Ictalurus punctatus; 2) Habitat quantification: to determine a habitat availability/flow relationship; and 3) Habitat isolation: to determine flow at which riffles serve 6