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u 1 1 1 1 1 1 1980, Hinckley et al. 1986}. Hinckley et al. (1986} divided freshwater fishes of the CRB into three major categories. The first group, big-river fishes, included largely endemic species that occur in large streams and rivers. The second group was described as endemic fishes occurring in small streams at low to intermediate elevations. The final group included fishes occupying mid- to high-elevation habitats with relatives co- occurring or present in adjacent drainages outside the CRB. Although also found in small streams, roundtail chub, flannelmouth sucker, and bluehead sucker can be classifed in the first group of mostly endemic, big-river fishes. Several morphological characteristics are common to the native, big-river fishes, including streamlined body forms, humped or keeled dorsal surfaces, leathery skins with fine or embedded scales, and large, often falcate, fins. These characteristics provide for improved swimming performance and stability in turbulent flows, which are common in much of the Colorado River and tributaries (Hubbs 1941, Hinckley et al. 1986, Hinckley 1991). Such morphologic features, combined with comparatively long life spans and breeding seasons initiated by water temperature and flow regime cues, may be adaptations to the harsh, unpredictable physical environment of CRB rivers and streams (Scoppettone 1988, Hinckley 1991, Stearns 1993). Prior to Euro-American settlement, the suite of native, big-river fishes present in the CRB were well-adapted to the environmental extremes of the basin, as several taxa have persisted for over 10 million years (Hinckley et al. 1986). Human Impacts If declines in big-river fishes over the past half century are any indication, human-caused changes have reduced the effectiveness of morphologic and life-history adaptations that allowed native fishes to thrive in the historically harsh, fluctuating environment of the CRB. In the late 1800s, settlers moving into the American Southwest demanded legislation to fund major water development projects. Since then, the water projects authorized by these acts and legislation (Table 2), and the agriculture, infrastructure, and Final Report September 2002