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270 Approximately 397 square miles along the upper 52 miles of the South Fork Salmon River drainage in west-central Idaho were included in the analvsis. Data were taken for 38 tributary streams, from 2,482,transects for aquatic and streamside environments, and from 291 areas for fishery conditions. Fishery , The drainage has historically contained the largest salmon run in Idaho com- posed entirely of summer chinook salmon. Steelhead trout, fluvial cutthroat trout, rainbow trout, Dolly Varden, brook trout, mountain whitefish, sculpin, and dace also occupy the study streams (Table 1). The study streams often have gradients that are too steep for high production of salmonids. However, salmonids have adapted to.almost all streams in the study area. Members of the Salmonidae family have been present since the Miocene--28 million years ago (Berg 1947). Consequently, salmonids have adapted their life cycle to survive under a dynamic, complex stream environment. They are well adapted to meet natural stress, but require certain conditions in their environmental niches to produce viable populations. Our methodology must be able to quantitatively describe these environmental niches over time and re- late these environmental conditions as to their control on fish populations. Once the environmental niches can be accurately described and evaluated, then the effect of streamflows on these niches can be predicted with validity. The study streams receive insignificant fishing pressure because of poor access and better fishing in surrounding areas. Thus, fish mortality is due almost entirely to natural causes, and standing crops thus provide a measure of fish populations under natural conditions, yielding unbiased estimators of the quality of the aquatic environment. Rainbow trout were the dominant species, possibly because the area con- tains both anadromous (steelhead trout) and resident species. Chinook salmon were second in.numbers and made unexpectedly heavy use of the small tributary streams for rearing their young. Dolly Varden were third, followed by west- slope cutthroat trout. Brook trout were fifth, approximately equaling the sculpin. Mountain whitefish were seventh in numbers, and dace were found only in one stream. Study Streams The average elevation of study streams is 5,653 feet and stream elevations range from 4,370 to 7,407 feet within 12 geomorphic types. An example of geo- morphic types present is land where alpine glaciation has created cirques or amphitheaters, stream gradients stairstep, and winter conditions are severe. ,