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>, Differing Methodologies and the Role of "Professional Judgment" Because I was specifically asked to review the methods that were used by the U.S. Fish and Wildlife Service for assessing instream flows, it appears that the efficacy of the various instream flow methodologies was not fully understood while studies leading to the recommendw flows were being conducted. Heavy investment in IFIM was made, and it clearly was not warranted. The method as currently formulated should not be used in the future in the potamon reaches of the Upper Colorado River Basin, owing to the problems I detailed above. Weaknesses in the IFIM approach were recognized as flow recommendations were developed and IFIM analyses were not used to support the flow recommendations on the Green and Yampa Rivers. Rather, ecological data and interpretations were couched in terms of "professional judgement" to provide rationale for the recommendations. On the Colorado River, IFIM analyses were used explicitly, along with reference to other studies which I summarized above (e.g., squawfish need clean gravel scoured by spring runoff and 180 - 220 C temperatures that usually occur on the declining limb of the runoff to spawn successfully). Use of IFIM on the Colorado River and discarding of it on the Green River raised doubts about the recommended regimes, which undermined the clear inference from the ecological studies that higher amplitude peak to baseflow regimes were needed. Moreover, emphasis on on "professional judgment" was overemphasized, given the general high quality of the ecological studies that were available. I agree with Tyus (1992) that considerations of in stream flow provisions were based on ecological information obtained in suboptimal habitats of these fishes. And, perhaps, the "biological opinion" process overshadowed the science. The recommendations should have been based entirely on inferences from long-term quantifications of energetics, habitat preferences, recruitment, channel geomorphology and food web composition and stability and simple correlations with the highly variable flows that eventuated over the decade of the 1980s. Had that been done, I think the flow amplitude recommended by the U.S. Fish and Wildlife Service on the Green River would have been higher (higher spring peaks, lower baseflows) and more consistent with my synthesis of the existing information. The Colorado 62