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GENERAL INTRODUCTION <br />The Colorado River Basin is located in the western United States. There are multiple <br />headwaters, including the Green River in Wyoming and the Yampa, White, and <br />Colorado Rivers in Colorado. The basin spans many miles flowing through parts of <br />Arizona, California, Colorado, New Mexico, Utah and Wyoming (Fig 1). The basin is <br />divided into the Upper Basin and the Lower Basin. The Upper Basin begins in Eastern <br />Wyoming and ends at Glen Canyon Dam in Lee's Ferry, Arizona. It runs 885 km north <br />to south and 563 km east to west (lorns et al. 1965) and covers 293,955 km2 (Upper <br />Colorado Region State-Federal Inter-agency Group 1971 a). The Lower Basin begins at <br />Lee's Ferry, Arizona and runs south to Mexico where it empties into the Gulf of Mexico. <br />Historically the Colorado River basin was a free-flowing contiguous system isolated <br />from surrounding river basins. Extreme seasonal and interannual variations in flow, <br />temperature, and turbidity, coupled with the geologic isolation of the Colorado River <br />Basin, allowed a very unique group of native fish to evolve. In fact, the Colorado River <br />basin has the highest percentage of endemic fish in North America (Hickman 1983). <br />Bonytail, roundtail chub (Gila robusta), humpback chub (Gila cypha), pike minnow <br />(Ptychocheilus lucius, formerly known as Colorado squawfish), Kendall Warm Springs <br />dace (Rhinichthys osculus yarrowi), Colorado River cutthroat trout (Salmo clarki <br />pleuriticus), razorback sucker (Xryauchen texanus), bluehead sucker (Catostomus <br />discobolus), flannelmouth sucker (Catostomus latipinnis) and speckled dace <br />(Rhinichthys oscielus) all comprise the historic fish community of the basin. <br />In the early 1960's the Colorado River Storage Act was passed which paved the way for <br />the construction of several large dams. These dams and many other types of water <br />impoundments were built from the northern to the southern end of the Colorado River <br />Basin to supply water and power to the human inhabitants of the west. With the advent <br />1