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25 historically occurred. Since the resultant composite hydrographs do not deviate significantly from the shape of the historical hydrographs, the water temperatures are not adversely affected. The warmer water temperatures in July and August combined with composite hydrograph might have a beneficial effect in initiating and lengthening the postulated spawning period of the Colorado squawfish. The minimum streamflow hydrograph requested by the Park Service is suitable for continued utilization of the Yampa River in the canyon by the Colorado squawfish. In contrast, a reduction of the upstream water temperatures with the corresponding reduction in water discharge would decrease the water temperature at Mathers Hole, adversely impacting the spawning habitat in the cobble reach. At the confluence of the Yampa and the Green Rivers, the water temperature response to reduced discharges in the Yampa River is complex and difficult to predict. Figure 20 shows that 1975 water temperatures just downstream of the confluence would be decreased by a maximum of almost 4°C. This would represent a water temperature reduction shock of almost 13°C between the two rivers for one specific time increment in the late summer. In 1983, however, the warmer water temperatures in the Yampa are a greater influence in warming the Green River than the discharge loss from the Yampa is in decreasing the water temperatures. The resulting water temperatures in the Green downstream of the confluence are warmer with the reduction of discharge in the Yampa. The warmer water temperature releases from Flaming Gorge Dam on the Green River decreased the water temperature difference between the Yampa and Green Rivers at confluence in 1983 compared to 1975. August 15 was designated as the end of the study period in this investigation based on the NPS minimum streamflow hydrograph. Following this date, the flows requested by NPS return to the base flows of 367 cfs. Based on Figures 20 and 21, it is recommended that this analy- sis be extended into the months of September and October when the larval Colorado squawfish enter the nursury stage following the downstream drift cycle of its lifestage. The possible water temperature difference shock late in the summer at the confluence may be detrimental to larval fish. Further, this analysis for the baseflow should be extended to the Jensen-Ouray area where the young-of-the-year seek nursery habitat. A constant baseflow of 367 cfs for the Yampa River should be reviewed for its possible adverse effects on the young-of-the-year lifestage of the Colorado squawfish in the lower Green River. 0 7 i