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the Blacksmith Fork River had a lower flow than the Logan River and the flows for both rivers were lower in 1976 than in 1975 because of a lighter snowpack. Streamflow at the study sites in both rivers were much lower than at the survey stations because of irrigation diversions (Figures 4 and 5). Water temperatures averaged weekly and the maximum-minimum values in 1976 were plotted for the Logan River in Figure 6 and for the Blacksmith Fork River in Figure 7. The mean and range of daily water temperatures for both rivers are provided for selected dates to show daily fluctuations in temperature by season (Appendix A; Figure l). In general, the water temperature of the Blacksmith Fork River was slightly warmer than the Logan River and the greatest fluctuation in water temperature occurred during the warmer summer months. The chemical analyses of the water in different years are provided for the Black- smith Fork River (Appendix A ; Table l) and the Logan River (Appendix A ; Table 2). The average conductivity for eleven measurements in 1975 was 488 microhmos (range 430-500) and for fifty measurements in 1976 was 479 micromhos (range 345-645) for the Blacksmith Fork River. The range of selected water chemistry parameters was compared for both rivers in Appendix A; Table 3. Waters with chemistry values such as these have been shown to be productive for brown trout, Salmo trutta (McFadden and Cooper 1964). The principal fish that inhabit the Blacksmith Fork and Logan Rivers are the brown trout and mountain whitefish (Prosopium williamsoni). In addition, large numbers of the mottled sculpin (Cottus bairdi) are found in these rivers, but were not studied because of the problems involved in making quantitative population estimates of this species. Cutthroat trout (Salmo clarki), rainbow trout (Salmo gairdneri), and speckled dace (Rhinichthys osculus) are found occasionally in the study areas of these rivers. In early spring, large Utah suckers (Catostomus ardens) migrate into and through the study sites, sometimes in large numbers. These fish are believed to migrate into these sections of the rivers for spawning, but no young suckers were found after the migration was over. Either the juvenile suckers migrated out of the study area or spawning was not successful if, indeed, it did occur. During the summer, small numbers of carp (Cyprinus carpio) and the Utah chub (Gila atraria) were sampled from the study sites. An ecological study of the mottled sculpin including age and growth, food habits, and reproduction was made on the Logan River east of Logan City, about 2.4 kilometers (1.5 miles) upstream from the Logan River control site (Zarbock 1951). This species may be important in the ecology of the rivers in the study area because it may compete with and provide forage for brown trout. Other aspects of the ecology of these rivers were studied at various times. For example, Beers (1969), Clark (1958), and McConnell (1958) studied the algal components of the river biota and Erman (1968), Hales (1955), Meyers (1972), and Pearson and Kramer (1972) investigated the insect fauna. In addition, various aspects of the ecology of brown trout and mountain whitefish were studied at different times and in different parts of the rivers (Bernard 1976, Bergersen 1973, Bridges 1963, Brown 1972, Gosse 1977, Kimball 1972, Mathews 1966, Meyers 1972, Mongillo 1976, Salevurakis 1974, Sigler 1951, Sigler 1952). Stream Alterations 6