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area above Henry's Lake. The South Fork of the Snake River and tributaries, from the confluence with the Henry's Fork to Palisades Reservoir, was treated as a sub-basin. Several drainages that flow into the Salt River originate in Idaho (e.g. Jackknife, Tincup, Stump and Crow Creeks). Those portions of these drainages, in Idaho, were treated as separate analysis areas. The lower portions of these sub-basins are bisected by the State boundary between Idaho and Wyoming. The amount of historic Yellowstone cutthroat trout riverine habitat within Idaho was estimated at 3,797 miles (Table 1). This amount included approximately 210 stream miles associated with tributaries to the Salt River and South Fork of Snake River that are occupied by the "finespotted Snake River" form. Also included was a minor amount (58 miles) of stream habitat associated with the Goose Creek and Raft River drainages located in Nevada and Utah (Personal communications with Mr. Gene Weller, Nevada Department of Wildlife and Mr. Kent Summers, Utah Division of Wildlife Resources). In addition to the riverine environments, 3 lakes (Henry's Lake and the two Palisades Lakes) were identified as being historically occupied. There is little historical information that quantifies trout abundance; most historic references provide an indication that trout were very abundant in upper stream reaches and common in lower areas (Gilbert and Evermann 1892; Rollins 1935). This current assessment (Table 1) indicates that approximately 1,622 miles of streams are presently inhabited by Yellowstone cutthroat trout (there was some uncertainty about the current status that precluded a determination in four of the sub-basins). Based on this information, approximately 43% of the historic habitat was felt to be currently occupied by Yellowstone cutthroat trout. Even though this occupancy value appears to be relatively high, caution should be applied before arriving at any final conclusions. Only a minor amount of genetic verification has occurred to date and there is a possibility that many populations have been influenced by rainbow trout hybridization. Visual, includ- ing meristic, determinations often preclude detection of rainbow trout contamination. The cutthroat trout in the headwater portion of Goose Creek, which enters the Snake River immediately above Shoshone Falls, has been shown through meristic evaluation (Personal Communication, Robert Behnke, Colorado State University)) and electrophoretic analysis (Personal communication, Gene Weller, Nevada Department Fish and Game) to be genetically pure. Other populations that have been electrophoretically verified, within the lower portion of the Snake River drainage, include Eight mile Creek (tributary to Raft River) and the headwater tributaries to the Blackfoot River. Exotic trout species were present in 19 sub-basins and these species were identified as being a potential threat in 16 sub-basins (Table 2). Rainbow trout were identified as being present in all 16 sub-basins and hybridization is a probable condition (Thurow 1988). There were nine (9) sub-basin identified as supporting populations of Yellowstone cutthroat of unknown status. With the exception of drainages reported by Thurow et aI. (1988) and several that were specifically addressed in the questionnaires, little quantification of population status (Table 2) exists and most of the information is based on qualitative appraisals of population health. Historical references relating to habitat condition, within the Idaho portion of the Snake River, are limited and largely qualitative (Gilbert and Evermann 1892). Gilbert and Evermann's description of habitat condition included temperature and substrate observations for both the Ross (probably Blackfoot River) and the Portneuf Rivers near their confluence with the Snake. For both streams, the summer afternoon water temperatures were observed in the mid to low 70's (F) and stream substrates had high levels of mud (probably sands and silts) along with gravels. Mink Creek, a tributary to the Portneuf River, was also described as having an afternoon water temperature of 59 F and a sand and gravel substrate. For all three streams, comments were made about dense growths of willows directly on the banks and within adjacent riparian areas. Trout were noted as being common in all three streams supporting the conclusion that habitat was in good condition and that occupancy was probable for the entire length of these streams. It is logical to conclude that other tributaries to the Snake also provided suitable habitat of similar quality characteristics. Current habitat assessment 16