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The Green River is also the largest tributary to the Colorado River, and extends about 800 km to its source, the Wind River Range in western Wyoming. The study area included the Green River from its confluence with the Colorado River {km 0) to its confluence with the Yampa River (km 552) in Dinosaur National Monument (DNM; Figure 1.). The Yampa River was also considered because the movements and distribution of the target fishes included both rivers, and flows of the Yampa River affect habitats of fishes in the Green River. The Green River above its confluence with the Yampa River has been influenced by operations of Flaming Gorge Dam since its completion and filling in 1963, and this area no longer supports endangered fish populations. Both Yampa and Green rivers contain relatively high-gradient reaches dominated by boulder, cobble, and gravel substrates {e.g., Cross Mountain and Yampa canyons, Yampa River; Whirlpool, Split Mountain, Desolation and Gray canyons, Green Riverj, and low-gradient alluvial reaches of meandering canyon and flat, open terrains dominated by finer substrates. The Yampa River, with an average annual discharge of about i.5 million-acre-feet, arises on the western slope of the Rocky Mountains near Steamboat Springs, Colorado, flows northward then westward, where it enters DNM and Yampa Canyon below its confluence with the Little Snake River. Upper Yampa Canyon (km 72-32) is a moderate gradient system characterized by rocky runs, shallow riffles, and rapids. The Yampa River begins to accumulate finer particles as it deepens, ' widens, and becomes slower moving to its confluence with the Green River at Echo Park. The Yampa River flows about 320 km and drops in elevation about 2,256 m (Joseph et al. 1977). Downstream from the Yampa River confluence, the Green River enters upper Whirlpool Canyon, a reach dominated by deep eddies, riffles, and boulder- strewn cliffs. The Green R1Ver then meanders through cottonwood, willow, and salt cedar vegetated sand and cobble shorelines in Island and Rainbow parks, entering Split Mountain Canyon at km 523. The river exits Split Mountain Canyon and DNM at km 510, and enters the Uintah Basin, where the river becomes very broad, shallow, and sandy. The Duchesne River, drainjng the southern slope of the Uintah Mountains, enters the Green River near Ouray, Utah (km 396.48). The White River, with headwaters on the .western slope of the Rocky Mountains, enters the Green River-just below the mouth of the Duchesne River., Below these large tributaries, the Green River proceeds 193 km through Desolation and Gray canyons, containing many rapids and deep pools. The Price River enters the Green River in lower Gray Canyon. The Green River then enters the Green River valley near 'the town of Green River, Utah, and receives the San Rafael River about 40.2 km further downstream. The Green River lastly passes through Labyrinth and Stil]water canyons in Canyonlands National Park, where it joins the upper mainstem Colorado River. The Green River drops in elevation about 3,048 km from its source to the Colorado River. Flows of most mainstream rivers of the Colorado River basin have been substantially altered by water development projects (figure 2). Examples of such alterations include modification of downstream flow and temperature patterns and channel morphology, and loss of upstream fish habitat due to stream blockage and inundation. Construction of Flaming Gorge and Fontenelle dams in the Green River in the 1960's reduced the magnitude of spring peak flows and increased baseflow at other times of the year. However, the magnitude and timing of spring and early summer peak flows in the existing 4