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279 streambanks dominated by brush. Rainbow trout used open areas more than cut- throat trout, which tended to utilize areas where timber dominated streambank cover. Populations of young-of-the-year chinook salmon were highest in the more open channels and lowest in channels where tree cover dominated banks. This is partially due to chinook salmon favoring the lower segments of tributaries (close to the river), which had larger areas of water surface per length of stream and lower channel gradients. Streambank cover explained 4 percent of the observed variation in total fish densities. Streambank condition ratings had no detectable influence and accounted for an insignificant amount of the explained variation of total fish popula- tion. Chinook salmon, cutthroat trout, Dolly Varden, sculpin, and mountain whitefish had about the same population means in areas of streams having un- stable banks as in areas having stable banks. Densities of rainbow trout increased with increasing streambank quality, but brook trout decreased. Pool and Riffle Relationship to Fish Populations Pool Quality--Pools of excellent quality had the highest population means and the greatest fish lengths per sample area. The higher population density was due, in part, to young chinook salmon utilizing the higher quality pools. Pool condition accounted for 8 percent of the chinook salmon's explained observed variation. Population density of rainbow trout and pool quality related inversely, as rainbow trout tended to occupy riffle areas that were combined with shallow pools. Dolly Varden, brook trout, sculpin, mountain whitefish, dace, and chi- nook salmon increased in population densities as pool quality ratings increased. Pool condition was second in importance in accounting for explained variations in total fish numbers. Pool Formation--Population means and explained observed variation demon- strated that pool formation factors were not significant determinants of the ability of a pool to support fish populations. The physical conditions of the pool itself exercise the more important influence. Pool-Riffle Ratios--Densities of fish populations in relation to pool-rif- fle ratios were lower than the often quoted optimum density at a pool-riffle ratio of 50/50. The highest total fish population densities occurred in areas of stream having 30 to 50 percent of the stream in pool. Study streams nat- urally contain infertile water and a lower pool-riffle ratio could be conducive to higher fish populations, as it would increase the proportion of the food- producing areas. Chinook salmon populations steadily decreased as percent of