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~ 9 GREEN AND VAMPA RIVER COMPLEX The Service considers the Vampa and Green Rivers as a system that is essential to the survival and recavery of the endangered fish, primarily because of their biologic and hydrologic interrelationships. The Green River above its canfluence with the Vampa River has been altered (hydrograph, temperature, sediment transport, fish habitat, and stream species composition) by canstructian and .operation of Flaming Gorge Dam. Vampa River flaws, however, remain predominately unregulated and follow a more natural hydragraph. Relative ta the Green River, the Vampa River has higher spring and summer water temperatures, and its input of sediment promotes the creation and maintenance of backwater nursery habitats far Colorado squawfish in the Green River. Operation of Flaming Gorge Dam has altered the magnitude, duration, and timing of the spring peak and has increased base flows in the Green River. This had negative impacts on the nursery habitat for Colarada squawfish and razarback sucker. Sediment and stream channel morphalogy in the Green River are maintained somewhat by spring runoff from the Vampa River (Tyus and Karp 1989). Sediment import into the Green River from the Vampa River contributes to the system's present sediment quasi-equilibrium (Lyons 1989). This sediment is important in creating backwaters and ather important habitats far endangered fish. The Green and Vampa Rivers also are interrelated biologically. Colarado squawfish migrate from the Green River to spawn in the Vampa River; the larvae are then transported back to Green River nursery habitats. Movement of adult endangered fish, between the Green and Vampa Rivers, was well documented by Tyus (1990), Tyus and Haines (1991), and others. ENDANGERED FISH The importance of the Green River to rare and endangered fish was established by the Recovery Program and recognized by many biologists as noted in the recovery plans for each of the species. The Green River and its tributaries were listed as the highest priority for recovery of Calorado squawfish in the Colorado River Basin in the recently revised Colorado Squawfish Recovery Plan (U.S. Fish and Wildlife Service 1991). The Green River in Desolation and Gray Canyons and in Dinosaur National Monument (Dinosaur) is considered extremely important in the recovery of humpback chub in the Humpback Chub Recovery Plan (U.S. Fish and Wildlife Service 1990a). The Bony tail Chub Recovery Plan (U.S. Fish and Wildlife Service 1990b) indicates that one of the last known riverine concentrations of bony tail chub was in the Green River within Dinosaur. In addition, the Green River supports the largest known population of razorback sucker in their natural riverine habitat (Lanigan and Tyus 1989).