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BACKGROUND Following the construction of Flaming Gorge Dam in 1962, the abundance of endemic fIsh species in the Green River has decreased. These species include the endangered Colorado squawfish (Ptychocheilus lucius), the humpback chub (Gila cypha), and the rare, but unlisted, razorback sucker (Xyrauchen texanus). The dam has altered the natural state of the Green River by reducing flood events and their severity, increasing late fall and winter fluctuations, and in general altering natural flows throughout the year (Tyus et aI., 1987). Studies conducted by the Fish and Wildlife SelVice (SelVice) have concluded that backwaters in the Green River serve as important nursery habitat for young-of-the-year Colorado squawfish (Tyus et aI., 1987; Tyus and McAda, 1984). The Remote Sensing Section, Research and Laboratory Services Division, Bureau of Reclamation (Reclamation), has been studying the use of remote sensing techniques and the effects of Flaming Gorge Dam releases on downstream fish habitat in the Green River since summer 1986 (Pucherelli et al., 1988, 1989a, 1989b; Pucherelli and Clark, 1989). Reclamation initiated an ISMP (interagency standardized monitoring program) for the upper basin reaches of the Green and Colorado Rivers, beginning at their confluence. Study parameters were collected in a standardized fashion and include various fish species and their habitats, including backwaters and side channels. This monitoring process will allow a correlation between fish capture data and the quantification of their habitat. Although aerial photography is currently the optimum method for mapping and determining various riverine habitat, the cost of this method is prohibitive for extensive studies. Consequently, a more cost-effective alternative for mapping backwater availability using videography was investigated during 1988 (Pucherelli and Clark, 1989). The investigation found that the quality of videography was sufficient to replace aerial photography for use in river monitoring studies. The objectives of this study were (1) to calculate backwater and side channel numbers and area and channel width by river-mile for four monitoring reaches on the Green and Colorado Rivers; (2) to correlate the river habitat data with CPUE (catch-per-unit effort) data collected by participating agencies - the SelVice, the Colorado Division of Wildlife, and the Utah Division of Wildlife Resources; and (3) to correlate backwater and side channel data with riverflow. Valuable information will be compiled to assist managers and researchers in facilitating the recovery of the endangered fish in the upper Colorado River Basin. METHODS Four study reaches were selected by the Service, Reclamation, and State wildlife agencies from Colorado and Utah in areas known to contain important backwater habitat for young-of-the-year Colorado squawfish: reach 1 - Colorado River from the confluence with the Green River to river- mile 110 (Cisco Landing); reach 2 -Colorado River, river-miles 140 to 170 (Ruby Canyon to Grand Junction); reach 3 - Green River from the confluence with the Colorado River to river-mile 120 (town of Green River, Utah); and reach 4 - Green River, river-miles 200 to 317 (beginning of Desolation Canyon to Split Mountain). River-mile designations were established by measuring distance along the center line of the river directly on GS (Geological SUlVey) 7.5-minute topographic quadrangles with a map wheel.