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. downstream water rights, (2) an additive flow requirement to offset consump- tive uses enroute, and (3) the complimentary instream flow requirement (Fig, 1). The most desirable total stream flow requirement is one that will satisfy several uses at once. Understandably, at a given location on a given stream, only certain uses may be relevant, or preferential consideration may be given to the use(s) regarded as most important. But in either event stream flow is apportioned through negotiation and compromise. A paramount concern in these deliberations is the ability to analyze the acceptability of incremental changes in stream flow with respect to a particular use, Instream flow assessments have traditionally arrived at a single thres- hold value for the fishery resource - "a minimum flow, II Such an instream flow recommendation was usually determined solely from an analysis of hydrologic records, and provided only a limited opportunity for negotiation. This approach is based on the mistaken assumption that only flows below this "minimum" will be detrimental to the fishery resource. As a result of the fallacies and weaknesses associated with traditional fishery assessments it was apparent that better methods were required, The IFG incremental methodology is a major advance in this regard for it attempts to quantify the amount of potential habitat available for each life history stage"of a species as a function of stream flow. This method is intended to be used as a decision-making tool and is specifically tailored to demonstrate the impact of incremental changes in stream flow on fishery habitat potential, The Incremental Methodology is intended to be used in those instances where the flow regime is the dominant determinant of the quality of the instream fishery or recreation resource and where hydraulic conditions are ~ 25 ~