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INTRODUCTION <br />Background <br />The Green River, in Daggett County, Utah, historically supported a <br />fish community predominated by native cyprinids and catostomids. Flaming <br />Gorge Dam, completed by the U.S. Bureau of Reclamation (BOR) in 1962, <br />trapped the river's suspended sediment and bedload, producing dramatic <br />increases in water transparency and resultant changes in channel <br />morphology in the tailwater. Immediately following closure of the dam, <br />water temperatures in the tailwater were nearly ideal for salmonid fish <br />species. In 1962, the Utah Division of Wildlife Resources (DWR) <br />established a tailwater sportfishery by stocking, primarily, rainbow <br />trout fingerlings. This put-grow-and-take program was initially <br />successful -- approximately 20% of stocked fingerlings eventually <br />returned to angler's creels at sizes averaging more than 300 mm total <br />length. As the reservoir filled, however, hydroelectric releases <br />increased to operational levels. Filling of the reservoir also caused <br />i <br />progressively colder water to be released through the fixed elevation <br />penstock inlets, from deeper in the reservoir's hypolimnion. Higher <br />discharges decreased ambient warming rates and protracted the effects of <br />cold release temperatures downstream. Excessively cold water <br />temperatures depressed trout growth and detracted from the tailwater's <br />recreational appeal. Consequently, the BOR and DWR cooperatively <br />conceived a plan to permit selective withdrawal of warmer surface water <br />from the reservoir. <br />BOR implemented the plan and modifications to the penstock inlets <br />were completed in June 1978. Steel intake extensions were fastened to <br />-9-