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. Introduction . . The Duchesne'River originates from headwaters on the south slope of the Uinta Mountains in northeastern Utah. It includes two major drainages, the Strawberry and Duchesne, which together encompass over 1000 square kilometers (4,247 square miles), Major tributaries to the Duchesne River include the Whiterocks River, Uinta River, Dry Gulch, Yellowstone River, Lake Fork, Rock Creek, North Fork Duchesne River, West Fork Duchesne River, Antelope Creek and the Strawberry River. Flows in the Duchesne River are affected by the Strawberry Aqueduct and Collection System (SACS) and Starvation Reservoir which are both components of the Bonneville Unit of the Central Utah Project (CUP). Starvation Reservoir, located on the Strawberry River approximately 6 miles upstream from the confluence with the Duchesne river, stores both Strawberry River and Duchesne River water and regulates flow into the lower Strawberry River. Water diverted from the Duchesne River at the Knight Diversion is delivered directly to Starvation Reservoir, The SACS diverts water from the West Fork ofthe Duchesne River and two of its tributaries, tributaries of the North Fork ofthe Duchesne River, Rock Creek, and several tributaries of Rock Creek (IABAT 1994). Operation of these CUP facilities and additional water depletions through several irrigation diversions results in daily, monthly, and yearly flow changes of the Duchesne River which have the potential to affect the quantity and quality of aquatic resources within the affected streams. The Duchesne River has changed significantly during the past 100 years. These changes can be correlated to changes in the hydrology of the river (Brink and Schmidt 1996). Duchesne River flows, unlike the Yampa River and White River, have been drastically altered, Total annual discharge of the Duchesne River has been reduced from historical levels of over 768,000 acre feet to approximately 400,000 acre feet (CH2M Hill 1997). The endangered Colorado pikeminnow (Ptychocheilus lucius) and razorback sucker (Xyrauchen texanus) along with native bluehead sucker (Catostomus discobolus), flannelmouth sucker (C. latipinnis), and roundtail chub (Gila robusta), listed as sensitive by the state of Utah, have been captured regularly in the lower Duchesne River (Archer et aL 1986, Cranney 1994), The lower 2.5 miles of the Duchesne River was designated as critical habitat for razorback sucker in 1994 (Fed. Reg.NoL 59, No. 54/Monday, march 21, 1994). Recent captures of Colorado pikeminnow and razorback sucker upstream of designated critical habitat (Cranney 1993) suggest that the Duchesne River may have a greater role in recovery than previously . . . . . . . 1 .