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I 25 desirable flow and temperature canditions for endangered fish. Existing stocks of some species of endangered fish are maintained in the Yampa River because of the more acceptable flow and temperature regimens (Tyus and Karp 1989). Reproduction of Calorado squawfish in the lower Green River cantinues because of ameliorating effects .of tributary flows, increased distance from Flaming Garge Dam, and past cooperative efforts by Reclamation in providing flows beneficial ta maintenance of the rare fish. However, bony tail chub (which are near extirpatian from the Upper Colorado River Basin) and razorback suckers (which have had virtually no recruitment) have continued to decline since t~e closure of Flaming ~orge Oam. Many factors influence the habitat needs of endangered and other native fish in the Green River, including time of year, life history stage, and habitat use of sympatric species. Flow, temperature, and other parameters associated with natural spring runoff influence the reproductive activities of Colorado squawfish, humpback chub, and razorback suckers. Maintenance .of low, stable flows in late summer and early autumn is conducive to successful recruitment in Colorada squawfish. High spring flows are believed to benefit all native fish. However, the timing .of high releases is critical. The abnormally high summer releases .of 1983 and 1984 fram Flaming Gorge Dam resulted in the almost total loss of two year classes. Law, stable winter flows through ice breakup are prabably important to overwinter survival of young and adults of native species, and very high winter flows may adversely affect endangered fish and could provide an undesirable winter refugium for some introduced fish. Alteration of historic flow regimens directly affected razorback sucker recruitment in the Green River basin as its continued survival in the wild is imperiled. Humpback chub are rare in Whirlpool Canyon of the upper Green River and their status and habitat needs in Desolation and Gray Canyons remain relatively unknown. Operation of Flaming Gorge Dam can be refined to lessen adverse impacts and to aid in the survival and recovery of the endangered Colorada River fish. Acceptable flows and temperatures will require twa major changes: (I) higher spring releases and (2) lower, more stable warm flows during the summer and autumn. SDriJ!.g Colorado Sauawfish The presence of adult Colorado squawfish in inundated shorelines and lowlands during spring runoff indicates that such behaviar, and associated feeding, may offset the large energy expenditure required for migration and spawning. Thus, natural flooding of lowlands in the spring and the consequent increased availability of faod and resting habitat appear important in the physiological readiness of adult Colorado squawfish. Migration signals the onset of the reproductive cycle in Colorado squawfish, and we consider migratian cues (e.g., high spring flows, increasing river temperatures, and possible chemical inputs fram flooded land) important to the maintenance of successful reproduction. Migration routes must be protected and barriers discouraged. The duration, magnitude, and timing of spring runoff also affect preparation of substrate for spawning and formation of eddy and pool habitats used by