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fisheries biologists. Instream flow may be defined as an adequate flow to a :,:;-:; The need for instream flows for fisheries is widely acknowledged tain the exis ting aquatic habitat and fish community in a particular stream ()r.. stream segment. During ~he past decade, a multitude of methods have been cleve'" loped to identify instream flow needs. Wesche and Rechard (1980) provide a sum- mary of major works on this topic. This proliferation of methods has not, however, resolved the issue of which method is best suited for particular situations. Several more recent papers (Nehring 1979, Prewitt and Carlson 1919, '~elson 1980, Loar and Sale 1981, and Hilgert 1982) have addressed this issue with varying degrees of success. Most such papers have focused on evaluating model mechanics (a necessary first step in model validation) and assumed that the most accurate hydraulic estimates could be equated with the best estimates of fishery flow needs. However, these studies failed to compare final recommendations of the various models on bases other than unquantified professional judgment or limited quantities of biological data. Compounding the difficulty in making precise methodological comparisons is the problem that some methods generate recommendations that are based on fairly subjective criteria. CL.:.ri,J The objectives of this study were to (1) develop more objective criteria for interpreting the results of somlil commonly used instream flow methods and (2) determine the bias of those and other methods relative to each other. Signifi- cantly unbiased methods were not construed to be "best methods." Rather the results were used to evaluate the general predictive tendencies of each method. no attempt to evaluate model mechanics as this subject has been ade- quately addressed by previous papers. ,. 2