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Executive Summary In commenting on the proposed plan. Gorman (Arizona Game and Fish) suggested that temperature controls could be an effective tool to reduce this thermal shock problem during the relatively short period of time that the humpback chub are descending into the mainstem (mid to late summer) without greatly favoring their competitors. Furthermore, once recruited. these long-lived native fish would potentially out-live their competitors by well over a decade. Fish and Wildlife Service Recommendation - According to the Fish and Wildlife Service's (FWS) biological opinion on the operation of Glen Canyon Dam, main channel spawning of endangered fish (critical habitat) is severely limited by cold-water releases from Glen Canyon Dam. In their biological opinion on the operation of the dam, the FWS's reasonable and prudent alternative recommended that Reclamation evaluate methods to control release temperatures and, if viable, implement controls. Reclamation agreed with this recommendation and included it in the U.S. Department of the Interior's (USDI) Final EnvirornnentaI Impact Statement (USDI 1995) and Record of Decision on the Operation of Glen Canyon Dam. Plan Development - This report integrates two purposes. planning and an envirornnentaI assessment of the alternatives. In Chapter II, the report summarizes Reclamation's study of various methods available to control temperature. Several designs were found to meet the temperature control needs of the project and are technically viable; however, costs varied significantly. The proposed alternative takes maximum advantage of the existing intake structures to reduce costs, yet meets the performance goals for temperature controls. This innovative approach would cost an estimated $15 million (to modify all eight intakes) and would be within Reclamation's spending authority. More traditional designs like those used at Flaming Gorge Dam and Shasta Dam would cost up to $149 million at Glen Canyon Dam, would have far exceeded Reclamation's spending authority, and would have required returning to Congress for legislation. The least costly method (the 4-intake modification at $10 million) was rejected by Reclamation because it lacked the flexibility needed to meet the downstream temperature objectives. Environmental Assessment - In Chapter III, the report compares the effects of the proposed warm(er)-water releases to those of the no action alternative (continued cold- water releases). It should be noted that although the proposed alternative is discussed as warmwater releases, in effect temperature controls would actually release water that is only about SOC (lOOF) warmer than the existing condition. To most rafters and recreationists, the water would still seem quite cold (S90F vs. 460F). The goal of the proposed alternative would be to modify Glen Canyon Dam to allow release temperatures to be controlled to improve conditions for endangered fish while at the same time protecting other important resources like the Lees Ferry trout fishery. The proposed plan would create a tiered (coldlwarmwater) fishery. Release temperatures would be increased from the existing levels (SOC-IOoC) to about ISoC during the summer months. This would improve temperatures for rainbow trout in the reach immediately below the dam (first 16 miles to Lees Ferry). Then, as the water flows 11