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All fishes require a variety of habitats throughout the year to complete their life cycle. Peak flows in spring reconfigure the channel and provide flooded bottomlands which are important for allochthonous input to the system (Stanford et al. 1996; Poff et al. 1997). Flooded bottomlands also provide resting areas for adult fish escaping fast water in the main channel and important rearing habitats for YOY fishes (e.g., Wydoski and Wick 1998). In the Colorado River basin, adult Colorado squawfish and razorback sucker use off-channel habitats extensively in spring (Osmundson et al. 1995). The low velocity and warmer water temperatures in off- channel habitats are hypothesized to assist with growth and gonad maturation during a time when river temperatures are still cool and high water velocities require increased energy expenditures. Flooded bottomlands are especially important to growth and survival of larval razorback suckers (Wydoski and Wick 1998; Modde et al. 1995). When flooded bottomlands are not available, other low-velocity habitats such as slow runs, pools, eddies, backwaters and flooded vegetation along the shoreline provide refuge from fast water in mid-channel habitats. However, these other habitats do not substitute for the productivity of flooded bottomlands (Wydoski and Wick 1998). Except for a transition period before and after spring runoff, base flows occur through most of the year (summer, fall, winter). Colorado squawfish preferred pools, eddies, and backwaters at moderate base flows and slow runs at very low base flows in the upper Colorado River (Osmundson et al. 1995). Razorback suckers also used pool and slow-run habitats during base flows. High-velocity or shallow habitats are generally not utilized except for briefi periods. However, shallow riffles or cobble bars are used for spawning by both species (Tyus and Karp 1990; Tyus 1991). Backwaters are important habitats for young of both species (Tyus and Haines 1991; Gutermuth et al. 1995). Throughout the year many different habitats are used by different life stages of the two species. Providing a variety of usable habitats in the appropriate spatial and temporal relationship will be important to recovery of these two endangered fishes in the Gunnison River. This study described the relationship between fish habitat and river discharge in the Gunnison River. The overall goal of this study was to quantify changes in fish habitat in the Gunnison River with changes in river flow and to use that information to assist with making flow recommendations for operation of the Aspinall Unit. The objectives of the study were: 1. Use a combination of airborne videography and ground truthing to quantify macro habitat at different flow levels. 2. Use channel cross sections to describe changes in river morphology over time. 2