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34~ it has deposited a large fan at its confluence with the South Fork. This damage was accelerated by the failure of beaver dams in the shale soils just beneath the volcanic cap. Other drainages have experienced similar erosion where beavers have been permitted to occupy streams flowing-through unstable shales. BIOLOGICAL FACTORS Fish populations.--Fish populations-were sampled by electro- fishing 1,500 foot sections at sample stations. 'The size-classes of fish sampled are shown in the Appendix F. Nearly 500 scale samples were taken, but the laboratory analyses had not been completed at the time this report was prepared. Brook trout were the most abundant species in Sweetwater Creek ' above Sweetwater Lake. Spawning brook trout were particularly numerous _ as they moved upstream from the lake in the fall; abundance of small fish indicated successful natural spawning. Rainbow and brown trout predominated at Stations II and III below the lake. sculpins were found in the lower Sweetwater, Stations II and III and suckers in Station III. Indications axe that a waterfall between Stations II and III has kept suc- kers below that point (Table 6). Rainbow trout exceeded all other species on the upper South Fork, Brook trout were fairly abundant; hrown and cutthroat trout were relatively scarce. No sculpins or suckers were seen. On the lower - South Fork, rainbow was the most abundant species with a few cutthroat netted. Whitefish and sculpins were common; brook trout, brown trout and suckers were not found. Hatchery-reared rainbow trout are stocked annually in both streams.