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1 <br />basin, major tributaries that formerly provided a variety of habitats to <br />which these fishes had unrestricted access have been partitioned by Flam- <br />ing Gorge, Taylor Draw, Redlands Diversion, and Price Stub Diversion dams. <br />In addition, operation of these and other dams and diversions further , <br />upstream has altered flow regimes in the downstream habitats of the rare <br />fish. The cumulative negative effects of such projects, in conjunction ' <br />with other man-caused changes in the river environment, may ultimately <br />lead to the extirpation of these endemic species. <br />The 15-Mile Reach <br />The upstream range of the Colorado squawfish and razorback sucker in the <br />Colorado River is delimited by the Price Stub diversion dam near Palisade, <br />Colorado (Fig. 1). The Redlands Diversion on the Gunnison River, 2.2 <br />miles upstream from the confluence with the Colorado River, blocks up- <br />stream movement of fishes in that tributary. A small, disjunct population <br /> <br />of adult Colorado squawfish still persists in the reach above the Redlands <br />dam, however. The stretch of the Colorado River between the Grand Valley <br />Diversion (River Mile 185.1) and the confluence with the Gunnison River <br />(RM 171.0), hereinafter referred to as the 115-mile reach,' experiences <br />man-caused alteration of its natural flow regime throughout the year. <br />Perhaps most important to the habitat of the endangered fishes is the <br />additional reduction in flow caused by irrigation withdrawals during <br />August-October, when natural flows typically are already low. Because the <br />15-mile reach is used by the Colorado squawfish and razorback sucker, ' <br />there is concern that additional flow-regime alteration may further <br /> <br />1