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Introduction <br />The Yampa River is the largest tributary in the Upper Colorado River Basin that <br />has a natural hydrograph and flows resembling historical magnitude (Tyus and Karp <br />1989). The Yampa River supports a self sustaining population of the endangered <br />Colorado squawfish (Tyus 1990) and one of five known endangered humpback chub <br />populations (Karp and Tyus 1990). In addition, the Yampa River contains one each of <br />only two know spawning sites of Colorado squawfish and razorback sucker (Tyus and <br />Karp 1990). Because most Colorado squawfish spawned in the Yampa River drift <br />downstream to nursery sites in the Unitah Basin, reproduction in the Yampa River is <br />important in defining squawfish recruitment in the Middle Green, White, and Yampa <br />rivers. Yampa River flows are highly variable annually with spring runoff peaks greater, <br />and summer base flows lower than the Green River in which it empties (USGS records). <br />Despite of, or because of, highly variable conditions native fishes are more abundant than <br />nonnative fishes in the lower Yampa River (Modde and Smith 1995). <br />In 1995, the Colorado Water Conservation Board filed on water rights to protect <br />the natural environment and habitats of endangered fish in the Yampa River (Filing # and <br />date). Since these water rights will be junior to existing rights, they will only influence <br />impacts from future water development. Existing instream flows in the Yampa River <br />appear to be adequate to maintain low but stable populations of Colorado squawfish and <br />humpback chub (Tyus and Karp 1989). However, in some years, for example 1994, <br />stream flows can be very low (approx. 10 cfs). The frequency and duration of low flow <br />periods is expected to increase with continued water development until the state of <br />Colorado develops its full allotment according to the Upper Colorado River Compact <br />agreement. Because limited opportunities currently exist to store spring runoff waters, <br />