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280 pool increased, because they required relatively larger streams in close proximity to the river that had lower percent pool. Rainbow trout had lower population means in areas having either a high or a low percent of pool. Their highest population densities occurred in con- junction with a 50/50 pool-riffle ratio. Dolly Varden was the only species to demonstrate a definite mean population increase as percent of pool increased. Cutthroat trout, brook trout, sculpin, and mountain whitefish did not show any marked trends. Pool and riffle only accounted for 2 percent of the explained observed variation and ranked seventh and eighth in importance. Effects of Stream Depth and Width on Fish Populations In the multivariate analysis, width was important in explaining variations among fish numbers per length of stream. Increasing depths and widths did not, however, have the same effects on all species. Cutthroat trout, Dolly Varden, brook trout, mountain whitefish, and dace had lower population means in the larger streams, which were dominated by rainbow trout and chinook salmon. Dolly Varden were the only fish found in the smallest streams, and cutthroat trout were collected only in stream areas less than 25 feet wide. Dolly Van- den and cutthroat trout did not increase in numbers as stream widths increased. Brook trout were found in the average width channels (6 to 9 ft), but not in smaller or larger than average stream channels. Chinook salmon, cutthroat trout, and sculpin numbers showed no relationship to changing depths. Stream depth was not significant in explaining variation in total fish populations. Relation of Stream Order to Fish Populations As stream order increased, available water space and total fish popula- tions increased. As stream order increased, numbers of chinook salmon, rain- bow trout, sculpin, and total fish increased per length of stream, and cutthroat trout and Dolly•Varden populations decreased. Streams classed as order 4 contained the most species. No species occupied all stream orders, although inadequate sampling in stream order 1 could bias this. Order 1 streams tended to be ephemeral and those with perennial flows were so small (average width 7 feet and depth 4 inches) that they were not sampled. Orders 4 and 5 contrib- uted about 75 percent of the fish population in the study streams, but only made up 19 percent of the stream mileage. Classifying streams in granitic lands as to their "order" and frequency t of occurrence can give the land manager information for an approximation of populations of fish species.