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<br />The apparent importance of variable, but clearly seasonal, flow regimes and associated <br />biophysical interactions were used as key rationale for the flow recommendations made by the U.S. <br />Fish and Wildlife Service. For the Yampa, Green and Colorado Rivers, flows were recommended <br />that would increase amplitude of the spring peak and reduce shon-term fluctuations from <br />- . <br /> <br />hydropower operations at baseflows. However, on the Green River, the peak flows recommended <br />for wet years were considerably less than flows of record and allowed substantial flow fluctuations <br />during the late summer, fall and winter (baseflow) period on all years. Moreover, a complex flow- <br />habitat model was used to support flow recommendations on the Colorado River, but model output <br />was discarded on the Green and Yampa Rivers. Review herein of models currently used to <br />mechanistically determine an incremental relationship between flow and river conditions favorable <br />to the endangered fishes revealed that none, including the one used on the Colorado River, were <br />sufficiently well developed to be used exclusive of many other ecological measures. <br />Inconsistencies in rationale and perceived need for a predictive model compromised the science that <br />strongly supported reregulation of flows in the Green and Colorado Rivers to produce more natural, <br /> <br />seasonal patterns. <br /> <br />Based on review of the ecological infonnation and recognizing the problems in the <br /> <br />methodological approaches that were used to derive flow recommendations, several key <br />uncertainties appear to be critical to the goal of establishing flow regimes that will ultimately recover <br />the endangered fishes. <br />· Flow seasonality and its correlates (e.g., temperature and physical habitat) may not be the <br />factor(s) limiting recovery of the native fishes. <br />· Given the high societal value placed on tailwater trout fisheries, and the high priority <br />placed on meeting entitlements under the Colorado compact and current water law (Le., the "law of <br />the river"), water volume in the Colorado and Green Rivers may be insufficient to produce flows <br />required to recover the fishes. <br /> <br />II <br /> <br />,. <br /> <br />.'. <br />