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<br />Various dams such as Flaming Gorge and Glen Canyon were built in the upper <br />basin that altered natural flow regimes, water temperatures, and turbidity. <br />These changes also resulted in direct loss of stream habitat due to unindation <br />by reservoirs and blockage of migration routes of the migratory Colorado <br />squawfish. The characteristic high spring and low winter flows have been <br />changed to relatively stabilized annual flows that display rapid daily <br />fluctuations (Vanicek, Kramer and Franklin 1970). Concurrently with these <br />environmental changes, various fish species have been accidentally or <br />intentionally introduced into the upper basin. By 1976, the Colorado River <br />Wildlife Council listed 20 species (40%) as native and 30 species (60%) as <br />introduced into the river system (Richardson 1976). About this same time, <br />Holden and Stalnaker (1975) reported 10 native fishes (34.5%) and 19 <br />introduced species (65.5%) in the mainstem of the Upper Colorado River Basin. <br />By 1982, the number of introduced species in the Upper Colorado River Basin was <br />76.4% of the 55 fish~s inhabiting the upper basin (Tyus et al. 1982). It is <br />believed that altered streamflows and water temperatures, and competition with <br />or predation by introduced fish were the main reasons for the decline of some <br />of the endemic large river fishes. <br /> <br />Recognition of Competion for Water Resources in the Colorado River <br /> <br />Drought conditions in the late 1800s followed by prolonged flooding in the <br />early 1900s stimulated the need for flood control on the mainstem Colorado <br />River (Fradkin 1981). The construction of Hoover Dam in 1935 and other dams <br />thereafter in the lower basin changed much of a free-flowing river to a <br /> <br />5 <br />