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Recent The occurrence of razorback sucker has been well documented in this reach since the 1960's (Binns 1965, 1967; Holden and Stalnaker 1975a, 1975b; Seethaler et al. 1979; McAda and Wydoski 1980). Although they have been considered rare in some portions of the Green River (Binns 1967), the upper portions of this reach supports the largest riverine population of razorback sucker remaining in the Basin, its numbers decrease below the Duchesne River (Tyus 1987; Lanigan and Tyus 1989). Description of Habitat: Historically, flows in the Green River began increasing in March, peaked in June, and remained high through July (Smith and Green 1991). The spring peak averaged about 8,000 cfs for the predam period of 1951-1962 at Greendale, Utah. Yearly and seasonal variation in this reach made flows highly variable. Mean monthly flow during spring runoff (April-July) was about 14,000 cfs. Construction of Flaming Gorge and Fontenelle dams in the 1960's altered hydrologic conditions in the Green River. The magnitude of the spring peak has been reduced, and flows during the remainder of the year have increased. The average spring peak measured at Greendale, Utah, has decreased to about 4,000 cfs; winter baseflows have increased about 50 percent (Tyus and Karp 1991). Additionally, temperatures and sediment transport have changed since construction of the dams. The flow, temperature, and sediment from the Yampa River somewhat ameliorate the reduction in spring flows from Flaming Gorge Dam (Tyus and Karp 1989). Depletions above and within this reach have the potential to reduce the total volume of water by 32 percent (USFWS 1992b). The Green River from its confluence with the Yampa River in Echo Park to Sand Wash includes several very different reaches. Substrate is a mixture of sand/silt with some large gravel/cobble riffles. After leaving the broad, shallow Echo Park reach, the river passes through Whirlpool Canyon, an area of steep cliffs, large pools, deep eddies, rapids, and large boulders. After exiting the canyon, the Green River flows through Island and Rainbow parks. The river in this area is shallow; backwaters, cobblebars, and side channels are common. Split Mountain Canyon contains large boulder fields, swift waters, and three large rapids. Some significant sandbars exist in the lower velocity sections of this area. The Green River, upon leaving Dinosaur National Monument at Split Mountain, enters the Uintah Basin where it becomes broad, shallow, and flat. The river is highly braided, and side channels and backwater nursery areas are prominent. Some drainage occurs due to agriculture, agricultural return flows, and urban discharge into the river. The substrate is sand underlain with rock. The Duchesne River, from the southern slope of the Uintah Mountains, enters the Green River near Ouray, Utah, RM 248. Just to the south, the White River flows into the Green River, and the river becomes deeper. However, it is still 49