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03/13/98 15:08 0 303 245 8933 FISH It WILDLIFE 444 R 0 4 Denver IM007/011 <br />during winter. Water temperatures have been reduced from historic temperatures <br />by a maximum of about 1.8°C in occupied habitat (McAda and Kaeding 1991). Tnese <br />modifications are typical of the ecological changes in a river after the <br />construction of a large dam (Vanicek et al. 1970). <br />Large dams and diversion structures can also be effective instreas barriers <br />that fragment stream reaches which can reduce the range of these native species <br />by precluding both young and adult fish from returning upstream after they have <br />migrated downstream. This affects species that migrate long distances to fulfill <br />life history requirements, especially the potamodromous Colorado squawfish (Tyus <br />1984; Tyus 1990). Instream barriers that divert water from main channel rivers <br />for irrigation and power generation have also served to reduce the range of these <br />species by rendering downstream reaches uninhabitable during low-flow perioas. <br />In upper basin rivers, this situation usually occurs downstream of diversion <br />structures during the mid-summer months of low-flow years when irrigation demands <br />are high. In some reaches, reduced water volume has lead to water quality <br />degradation by increasing the water temperature and elevating concentration <br />levels of human-produced and naturally occurring trace elements (e.g.. pesticides <br />and selenium) above the species tolerance threshold, and simplification or <br />elimination of adult habitats. During extreme low-water years, some reaches have <br />entirely been dewatered for several continuous days during summer months <br />resulting in loss of habitat, loss of migratory corridor, and possible stranding. <br />The Intent of the Recovery Implementation Program (RIP) is to bring abou. <br />the recovery and delisting of the endangered fishes while allowing upper basin <br />states to develop their entitled water under the Colorado River Compact. An <br />important component of the Recovery Program is the determination of flows needed <br />for recovery of these fishes. Furthermore, legal protection of sufficient <br />instream flaws for the maintenance and enhancement of riverine habitats to <br /> <br />i