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<br />1 <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br />urban developments associated with the water projects, have dramatically altered riverine <br />environments. <br />Table 2. Acts and legislation passed to develop and manage CRB water resources.* <br />Act Date Passed Effect ___ <br />Reclamation Act 1902 -Allowed federally subsidized urigat~on <br /> projects <br />Colorado River Compact 1922 -Apportioned Colorado River water to upper <br /> and lower basin states <br />Boulder Canyon Act 1928 -Official approval of the Colorado River <br /> Compact; authorization of Boulder Dam and <br /> All American Canal construction <br />Mexican Water Treaty 1944 -Guaranteed Mexico a minimum of ] .5 <br /> million acre-feet of Colorado River <br /> water annually <br />Upper Colorado River Compact 1948 -Divided Colorado River water between <br /> upper basin states <br />Colorado River Storage 1956 -Autharized four major storage units in the <br />Project Act Upper CRB <br />Colorado River Basin 1468 -Authorized the Central Arizona Project; <br />Project Act assigned priority to water users; and <br /> attended to other administrative details <br />Colorado River Basin 1974 -Assured maintenance of water quality <br />Salinity Control Act standards for water delivered to Mexico <br />*Source: Wegner 1989 (For details see also Carlson and Muth 1989). <br />Physical alterations-At least 140 dams and diversion structures are present on major <br />rivers and tributary streams throughout the Colorado River Basin (Bishop and Porcella <br />19$0). For major CRB rivers, Bishop and Porcella (19$0) estimated that 22% of <br />historically lotic reaches have been converted to reservoirs. In addition to loss of lotic <br />habitat through inundation, dams also modify sediment dynamics and downstream <br />hydrograph and temperature characteristics (Collier et al. 1996). <br />' Typically, dam-caused changes in the temperature, timing, and magnitude of streamflows <br />negatively affect distribution and survival of warm-water adapted native fishes. <br />Tailwaters of hypolimnial-release dams are often too cold far successful reproduction by <br />native warmwater fishes (Vanicek et al. 1970, Holden and Cast 1981, Marsh 1985, <br />Valdez and Ryel 1995, Bestgen and Crist 20p0). Cooler water temperatures also <br />influence growth and survival of embryos and young fish. Larvae grow more slowly, <br />' which increases their risk of predation and decreases accumulation of energetic reserves <br />' Final Report September 20(12 <br /> <br />