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<br />INTRODUCTION <br /> <br />The Yampa River is the largest tributary in the Upper Colorado River Basin that has a <br />relatively natural hydrograph with flows resembling historical magnitude (Tyus and Karp 1989), <br />Yampa River flows are highly variable annually with spring runoff peaks greater, and summer <br />base flows lower than the Green River into which it empties (USGS records), Self sustaining <br />populations of the endangered Colorado squawfish Ptychocheilus /ucius (Tyus 1990) and one of <br />five known endangered humpback chub Gila cypha populations (Karp and Tyus 1990) reside in <br />the Yampa River. In addition, this river contains one each of only two know spawning sites of <br />Colorado squawfish and razorback sucker Xyrauchen texanus (Tyus and Karp 1990), Because <br />most Colorado squawfish spawned in the Yampa River drift downstream to nursery sites in the <br />Unitah Basin, these offspring are important in defining squawfish recruitment in the Middle <br />Green, White, and Yampa rivers, Despite, or because of, highly variable environmental <br />conditions, native fishes are more abundant than nonnative fishes in the lower Yampa River <br />(Modde and Smith 1995), <br /> <br />In 1995, the Colorado Water Conservation Board filed on water rights to protect the <br />natural environment and habitats of endangered fish in the Yampa River (Case numbers <br />95CWI56 and 95CW155, filed December 28, 1995), Since these water rights will be junior to <br />existing rights, they will only influence future water development. Existing instream flows in the <br />Yampa River appear to be adequate to maintain low but stable populations of Colorado <br />squawfish and humpback chub (Tyus and Karp 1989), However, in some years, for example <br />1994, stream flows can be very low (approx, 10 cfs), The frequency and duration oflow flow <br />periods are expected to increase with continued water development until the state of Colorado <br />develops its full allotment according to the Upper Colorado River Compact agreement. Because <br />limited opportunities currently exist to store spring runoff waters, the greatest opportunity for <br />water depletion occurs during the low flow periods of the year, exacerbating potential low flow <br />impacts on fish. <br /> <br />If the anticipated frequency of low instream flows cannot provide adequate protection of <br />endangered fish, it is incumbent upon the participants of the Recovery Implementation Program <br />for the Recovery of the Endangered Fishes of the Upper Colorado River Basin (RIP) to provide <br />alternatives for the recovery of affected listed species. Options to provide adequate flow <br />protection include purchasing and converting existing senior water rights to instream flow rights, <br />or to develop water storage for augmenting flows during the low flow period. Enlargement of <br />Elkhead Reservoir, on Elkhead Creek, could store up to 25,000 acre feet of water during spring <br />runoff for flow augmentation in the summer, but would cost nearly 30 million dollars (Maddux, <br />pers, comm,), However, the benefits of providing baseflow augmentation compared to the cost <br />of retaining spring high flows for endangered fishes is uncertain, <br /> <br />In an effort to address the future water development and recovery options for endangered <br />fishes in the Yampa Valley, the RIP initiated the Yampa River Basin Endangered Fish Recovery <br />and Water Management Plan, The goal of this plan is "to provide water for existing and future <br /> <br />5 <br />