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ABSTRACT Describes the "Montana Method," a quick, easy methodology for determining flows to protect the aquatic resources in both warm- water and coldwater streams based on their average flow. With this method, biologists do their analysis with the aid of hydro- logical data provided by the U.S. Geological Survey. Detailed field studies were conducted on 11 streams in 3 states between 1964 and 1974, testing the "Montana Method." This work involved physical, chemical, and biological analyses of 38 different flows at 58 cross-sections on 196 stream-miles, affecting both coldwater and wannwater fisheries. Reports or publications on 6 study streams are available. Numerous black and white photos and 35 rom. slides were taken of all the flow stages studied at each cross- section. The studies were all planned, conducted, and analyzed with the help of state fisheries biologists. Results reveal that the condition of the aquatic habitat is remarkably similar on most of the streams carrying the same portion of the average flow. Similar analyses of hundreds of additional flow regimens near U.S.G.S. gages in 21 different states during the past 17 years substantiated this correlation on a wide variety of streams. Running waters studied ranged from small precipitous brooks high in the Rocky Mountains to large, low-gradient rivers and streams out on the prairies of mid-America or along the coastal plains. Results are consistent from stream to stream or state to state, and it is impossible to get a zero flow recommendation using this method. Ten percent (10%) of the average flow is a minimum instantaneous flow recommended to sustain short-term survival habitat for most aquatic life forms. Thirty percent (30%) of the average flow is recommended as a base flow to sustain good survival habitat for most aquatic life forms. Sixty percent (60%) of the average flow is recoTID'Ilended to pro- vid~ excellent to outstanding habitat for most aquatic life foTITIS during their primary periods of growth and for the majority of recreational uses. Thirty pages illustrated with tables, graphs, and photos. .., "