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characterized by eddies, backwaters, side channels, and some pools. The substrate is predominantly sand/silt. This reach of the Green River ends near Sand Wash above Desolation Canyon. Relationship to Constituent Elements: Water Flows in this reach are dominated by releases from Flaming Gorge Dam and flows from the Yampa River. During an average hydrologic year, spring peaks of about 13,000 cfs will occur at Jensen, due to an average peak flow of 8,000 cfs from the Yampa River and 4,700 cfs from Flaming Gorge Dam. Flows above about 16,000 cfs are needed to inundate bottomlands. Because of the distance between this reach and the dam and unregulated flows of the Yampa River, near-historical water temperature levels in this reach can be achieved for the fish. However, when summer and fall cold water releases exceed downstream flows, water temperatures will be depressed. Surveys from this portion of the Green River indicate that the concentrations of boron, selenium, and zinc in the water, bottom sediments, and biological tissue are sufficiently large to be harmful to fish (Stephens et al. 1988, 1992). This study detected increasing concentrations of selenium in the water from near the detection level of 1 µg/L at Greendale to a mean of 2 µg/L by Green River, Utah. Large concentrations of selenium were present in water discharged from Stewart Lake (mean 6.7 µg/L) and Ashley Creek (mean 88 µg/L). Selenium concentrations in return flows to the Green River have been shown to cause direct mortality on razorback sucker larvae (Bruce Waddell, USFWS, pers. comm.). Physical Habitat Adult razorback suckers overwinter in the Jensen and Island and Echo Park reaches of the Green River (McAda and Wydoski 1980; Valdez and Masslich 1989). Adults are attracted to the large backwaters, tributary mouths, and flooded bottomlands within this reach in early spring prior to spawning (Tyus and Karp 1990). Spawning habitat includes cobble/gravel bars in Echo Park and from Ashley Creek to the lower boundary of Dinosaur National Monument (Tyus and Karp 1990). During high water years, adults in reproductive condition also are found in flooded bottomlands and tributary mouths within this reach (Tyus and Karp 1990). These types of areas provide warmer water temperatures, rich feeding areas, low- velocity habitat, and potential spawning and nursery habitat. This important reach contains high-quality nursery areas for the endangered fishes in the Green and Yampa Rivers. These include the mouths of backwaters, bottomlands, wetlands, and tributary streams. These same areas also are used by adult razorback sucker for feeding both pre- and post-spawning periods. 50