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4' ECOLOGY OF RIVERINE FISHES IN REGULATED STREAM SYSTEMS 67 Gorge Dam between 1962 and 1966 were relatively low to allow the reservoir to fill. These low flows were warmed by ambient condi- tions, so summer temperatures were increased from about SOC to near 130C shortly below the dam. After 1966, the releases were doubled and ambient warming was reduced to only a few degrees. This change in flow, and the resultant temperature change, reduced the tailwater trout fishery substantially and also eliminated successful reproduc- tion of Colorado squawfish for 40 additional kilometers below the dam (Holden and Stalnaker, 1975; Holden, 1977; Holden and Crist, 1979). The Bureau of Reclamation installed inlet modifications on Flaming Gorge Dam in 1978 to draw water from higher, warmer levels. This project was initiated to help the failing tailwater trout fishery. It is expected that the warmer summer flows will also bring back successful reproduction of Colorado squawfishto the 40 km of river mentioned. Studies are being conducted to monitor the effect of the inlet modification on both the trout fishery and the native warm-water species. If this project is successful, it may provide a methodology for alleviating negative temperature problems below other dams. Changes in native fish populations in the Colorado River system caused by changes in turbidity-water chemistry or gas super- saturation have not been documented. The Colorado River historically fluctuated tremendously in turbidity and water chemistry, therefore, it is probable that the native species are fairly well adapted to extremes in these parameters. Gas supersaturation, caused by spillage over the dam, has occurred at Navajo Dam, with resulting kills of planted trout (W. McNall, pers. comm., New Mexico Game and Fish Department, Santa Fe). The effect of reduced flows on the Colorado River fauna has not been adequately studied. The Colorado River Storage Project dams reduced flows significantly in all of the upper basin. Flows were reduced most drastically in the San Juan River and the Gunnison- Colorado rivers (Joseph et al., 1977), where mean monthly May flows were reduced to the lowest levels on record, even lower than the drought years of the 1930s. Flows in the Green River were not as severely reduced, primarily because of the natural inflow of the Yampa and White rivers, two of the three non-regulated large trib- utaries in the entire Colorado River system. Colorado squawfish still reproduce successfully in much of the Green River (Holden and Stalnaker, 1975; Holden, 1977; Holden and Crist, 1979), but repro- duction in the Colorado River has not been documented since 1964 (Taba et al., 1965; Holden and Stalnaker, 1975; Seethaler, 1978). No studies have been conducted to determine reasons for this loss of reproduction. Temperatures in the Colorado River remain normal.