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5 September) and winter (December through February). During these periods water releases from Flaming Gorge Dam fluctuate within the operational constraints of the powerplant (800-4,700 cfs). Flaming Gorge Reservoir results in an estimated annual depletion of 78,300 acre-feet due to evaporation. The mean annual flow of the Green River, near Jensen, Utah, is almost the same now as prior to the construction of Flaming Gorge Dam, but: the flows and temperatures are significantly changed from historic patterns. In general, spring peak flows are much lower, while late summer and winter flows are higher, than historic averages. Minor peaks in discharge occur in summer and winter corresponding to peak power demands, while base flows are generally elevated during the remainder of the year to accommodate winter reservoir drawdown and minimum flow agreements. Flaming Gorge operations are within the general framework of the above criteria, but vary year to year based on hydrologic conditions. Historical and post-Flaming Gorge flows differ significantly (Figure 1). Historically, flows in the river increased with the onset of snowmelt in March, peaked in June, and remained high through July. The mean annual spring peak for the historic period, measured at Greendale, was about 7,800 cfs. Following spring runoff, flows declined to less than 1,000 cfs for the remainder of the year. Variations of this pattern occurred during wet and dry historic periods. Reservoir filling occurred from 1963-1966 with the first full year of operation beginning in 1967. In 1979, Reclamation began releasing water through the multilevel outlet structure which provided warmer water for fish. Operations changed in 1985, when the Service and Reclamation signed an agreement" for protection of critical endangered fish nursery habitats downstream of Jensen, Utah, and for other special releases associated with study objectives contained in the interagency agreement (6-AA-40-04070). BASIS fOR OPINION The endangered Colorado squawfish, humpback chub, bonytail chub, and razorback sucker inhabit the Green River. Occupied habitat currently extends from the confluence with the Colorado River at river mile zero (0) upstream to near the Willow Creek confluence (Swallow Canyon) at river mile 383.5. The main stem Green River and its tributary, the Yampa, contain the largest populations of Colorado squawfish and razorback sucker known to exist in natural riverine habitats. Humpback chub have a limited, discontinuous distribution in canyon- bound habitats and persist in small numbers in Desolation and Whirlpool -- Canyons. The bonytail chub is extremely rare throughout the Upper Colorado River Basin.