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31 large slow moving backwater areas to narrow, deep and turbulent rapids. Shallow riffle areas were often present above deep pools and alongside the main river channel. Below Atches Wash the river became wider and much more uniform in depth and flow as the river progressed downstream to the confluence of the Green River. As the diversity of the river habitat decreased there was a corresponding increase in numbers of exotic fish. The White River below Mountain Fuel Bridge is utilized for irrigation, an activity which Seethaler et al. (1979) have suggested may be a possible cause for deterioration of river habitat in the upper Colorado River Basin due to increased leaching of the soil. This results in increased salinity through return flows and changes in water quality due to the addition of fertilizers, pesticides and other materials. As the physical and chemical characteristics of the Colorado River Basin are changed by man's activities, exotic fish can be expected to become more and more abundant (Berry, 1979). Different types of sampling methods may be selected for a specific size or species of fish. By using different sampling methods in this study, more accurate data on fish species composition and relative abundance was obtained. For example, sampling with the electrofishing boat showed a strong bias toward larger fish, especially flannelmouth suckers, because of 1) the locations sampled, 2) the larger fish's susceptibility to the shocking gear, and 3) the fact that large fish were easier to see in the turbid waters (Table 3). Prewitt et al. (1978) also used an electrofishing boat for collecting fish in the Colorado portion of the White River ahd also found large flannelmouth suckers to be the most abundant fish (Table 3). In this study, that bias was reduced by using the shocking-seining technique which was more selective for small fish (Table 3). Larger fish were apparently able to detect the electrical field and/or sein enabling them to escape.