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. ,. . ..... _,-,,' ,"-..-_.e_\"~,~>.,..~.)_r"",",,",,~':.,". ,~,-~,_--'"'__-.",_^,A<~,_,,~ - e e .. impoundment seasonal temperature pattern resembled the pre- impoundment pattern, but temperatures after 1962 were slightly lower in the summer months and higher in the winter months than before impoundment (Table 2)_ Maximwn summer water temperature, was inversely related to stream flow. In 1963 and 1965, summer discharges from the dam were relatively low (102-1,439 cfs; Table 1), and water temperatures from Bridgeport downstream to Jensen approximated pre-impoundment con- ditions (Table 2). The temperatures of the Green and Yampa Rivers were nearly identical at their confluence at Echo Park in 1965 (Figure 2). In 1964 and 1966, however, sununer discharges from Flaming Gorge Dam were higher (1,466-2,441 cms; Table 1), and water tem- peratures were lowered a greater distance downstream. At Echo Park the Yampa River inflow was much warmer than the receiving Green River waters (Figure 2). In these years the Green River at Island Park had warmed considerably (Figure 2) but had not reached pre- impoundment mean temperatures at the end of the study area at Jensen (Table 2). The inverse relationship between discharge and water temperature was especially apparent at Little Hole and Bridgeport, 7 and 17 miles below the dam, respectively (data from Utah State Department of Fish and Game recording thermometers). During the summers of 1963 and 1965, maximum water temperature at Little Hole was 63 F and 59 F, respectively, while during summers of 1964 and 1966, maxi- mwn temperature was 53 F and 55 F. At Bridgeport, maximwn swn- mer water temperature in 1963 and 1965 was 76 Fand 68 F, respec- tively, and in 1964 and 1966, 58 F and 60 F. Water Chemistry.-A comparison of pre-impoundment and post- impoundment water chemistry data from USGS records on mean an- nual values of bicarbonates, total dissolved solids, specific conductance, and pH at Greendale and Jensen did not reveal any permanent change in these aspects after dam completion (Table 3). In the 1963 water- year, the first year after dam closure, however, the values of bicar- bonates, total dissolved solids and specific conductance were much higher than in the other years. These high values were probably the result of the extremely low flow of that year (mean flow =231 cfs) due to the fIlling of Flaming Gorge Reservoir. In general, the water chemistry determinations made during the fish collections in the pres- ent study gave results similar to those reported ~y pre-impoundment surveys. Suspended Sediment and Turbidity.-The Green River at Green- dale was nearly sediment-free but increased in silt load progressively 303 Ii 11 L ,! ,1 '1 " +- J ,