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269 i Ahnell (1964), and Hall and Lantz (1969) associated low standing crops of trout with increase in fine channel sediments. Burns (1971) found only living space correlated significantly with biomass. Saunders and Smith (1955) found that cover was the dominant factor in increasing standing crops of brook trout. Hunt (1971), in conflict with Chapman (1966), noted that the carrying capacity for trout was poorly correlated with the surface area, but that an increase in permanent bank cover increased fish biomass. However, Ruggles (1966) found that silver salmon fry avoided shaded areas and their density decreased when artificial cover devices were added. Needham and Jones (1959), however, demonstrated that rainbow trout strongly preferred sheltered areas. Reid (1961) stated that the choice of physical factors to be analyzed is difficult because environmental variables in streams are typically correlated and confounded with one another. Later studies lent credence to Reid's think- ing on multivariable control of fish populations. Lewis (1967) measured six physical characteristics of 19 pools and found they accounted for 77 and 70 percent of the variation in number of brown and rainbow trout, respectively, in pools. Stewart (1970) analyzed 15 physical aquatic structural character- istics and found mean depth was the single variable of first importance; in addition the combination of several categories of hiding and protective cover proved to be highly correlated with the distribution and density of brook trout, but not rainbow trout. Lewis (1967) concluded that surface area, water volume, average depth, average current velocity, and percent of cover accounted for variations in numbers of trout. The literature demonstrates the complexity to be faced in the development of a valid methodology. When the multivariable controls on the aquatic system from its surroundings are combined with in-stream controls and then combined further within the different aquatic types that can change the importance of any given variable, it is understandable why a methodology of high validity to determine aquatic-fishery relationships has not been developed. The study summarized here provides some information from mountainous aquatic environments, in specific geomorphic settings, that can be used to examine the validity of a methodology to evaluate quantitatively the aquatic conditions and their control of fish populations. There also may be an in- fluence from chemical conditions, but it was not addressed in this study. STUDY AREA The study area is in the southern portion of the Northern Rocky Mountain physiographic province and located entirely within the Idaho Batholith.