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INTRODUCTION Historically, floodplain habitat in low-gradient reaches of the middle Green River was inundated regularly during peak spring flows. Bankfull flows at the Ouray National Wildlife Refuge averaged 575 m3ts (Flo Engineering 1996) and were historically exceeded 2 of every 3 years (USGS Jensen Gage data between 1947 and 1962). After closure of Flaming Gorge Dam, bankfull flows were exceeded only 1 in every 4 years (U.S.G.S. Jensen Gage data between 1964 and 1992). Reduced peak flows since the closure of Flaming Gorge Dam have altered main-channel morphology (Andrews 1986), influenced the chronology of the hydrograph (Tyus and Karp 1989), and reduced floodplain connectivity with the Green River (Irving and Burdick 1995). During the high spring river flows, adult razorback sucker Xyrauchen texanus have been collected from floodplain habitat (Tyus and Karp 1989, 1991). The significance of floodplain habitat to the species biology is unknown. High spring flow events have been correlated with recruitment in adult razorback sucker (Modde et al. 1996), but the relationship is undefined. Based on anecdotal and observational inferences that floodplain habitat was important to both early and adult life stages of razorback sucker and Colorado squawfish (Tyus and Karp 1989, 1990), this project was designed to evaluate river-use patterns by adult razorback sucker during the spring in the middle Green River, initiate pilot studies to evaluate potential benefits of floodplain wetlands to immature razorback sucker, and define flows necessary to connect Old Charley Wash wetland to the Green River. Specific objectives of this project were to 1) describe movement and habitat use patterns of adult razorback sucker, 2) describe the growth and survival of immature razorback sucker in wetlands relative to main-channel habitat, and 3) determine flows required to inundate Old Charley Wash. Because of the unrelated nature of the above studies, this report has been organized into separate chapters. STUDY AREA The study area included the Green River between the lower end of West Branch (RK 391, river kilometer upstream from the confluence of the Green and Colorado rivers) to its confluence with the Yampa River (RK 555) (Figure 1). This reach represents the upstream portion of the longest, low-gradient section of the Green River below Flaming Gorge Dam occupied by endangered fishes and has the greatest area of floodplain habitat in the Green River drainage (Irving and Burdick 1995). The magnitude of spring flows through the study area are determined by the relatively natural hydrograph of the Yampa River and summer flows of the Green River regulated by Flaming Gorge Dam. The presence of Flaming Gorge Dam has reduced both variation and magnitude of the annual hydrograph in the Green River (Tyus and Karp 1991), reducing the historic width of the river channel and its ability to transport sediment (Andrews 1986). In addition to physical changes in the historic habitat, the 9