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RESULTS Discharge Discharge was calculated by adding Green River discharge measured at Green River, Utah (188 km upstream from the confluence) with Colorado River discharge measured at Cisco, Utah (156 km upstream from the con- fluence) (USGS, 1980-81). During the 1980 sampling season, (April 26 - June 18), discharge ranged from 681 m3/sec (24,000 cfs) to 1,806 m3/sec (63,790 cfs) and averaged 1,280 m3/sec (45,203 cfs). Discharge during the same period in 1981 ranged from 198 m3/sec (7,000 cfs) to 655 m3/sec (23,120 cfs) and averaged 378 m3/sec (13,352 cfs) (Figure 4). Reduced discharge during 1981 caused several changes in the mixing zone of the river and reservoir as discussed in the Introduction. Temperature Spanish Bottom Shortly after sampling was initiated in 1980, surface water temper- ature decreased from 14.4°C to 11.1°C, remained cool for several days and then began a slow warming trend (Figure 4). Surface temperature increased from 15°C to 17.2°C during the 1981 sampling period. Inasmuch as striped bass spawn in most rivers at temperatures between 15.6 and 17.8°C, temperatures during the 1981 sample period were suitable for spawning but not during the 1980 period. Gypsum Canyon Surface water temperature at Gypsum Canyon varied from 12.8 to 17.2°C during the 1980 sample period (Figure 4). Water temperature at Gypsum in 1980 was within the range of temperatures normally present during