Note: For many non-migratory species, occurrences are roughly equivalent to populations.
Estimated Number of Occurrences: 21 - 300
Comments: It remains in portions of the Snake River system, namely the Okanogan River in Washington, and Clearwater River, Hells Canyon and middle Snake River in Idaho, but is extirpated from many former locations (Frest and Johannes, 1995). It also occurs in the Klamath River drainage in California and Oregon (Frest and Johannes, 1995) and Umpqua drainage in Oregon (Frest and Johannes, 2000). A recent survey of 115 sites in the Plumas, Tahoe, and Eldorado National Forests plus Lake Tahoe Basin management unit found it in only 1 site in Plumas NF (1 of 70+ streams) (Howard, 2008). Recently in California: Fall River, Pit River, Scott River, Klamath River, Napa River, and Shasta River (Howard, 2010). It is absent from the Olympic Mountains, Washington and points north but occurs sporadically in Willapa Hills (southwestern Washington) and northwest Oregon, and occurs more continuously from southwest Oregon south to southern California (COSEWIC, 2003). In Oregon, populations were recently confirmed in the Middle Fork John Day River and the lower main stem of the Umatilla River (Brim Box et al., 2003; 2006). Hovingh (2004) found it in abundance in the Humboldt River drainage (Lahonta basin) in northern Nevada (this population may have been overlooked in the past). Karen Mock (Utah State University, pers. comm., 2007) has collected specimens from the Chehalis River, Similkameen River, and Toppenish Creek in Washington; and Umatilla River, Middle Fork John Day River, and Owyhee River in Oregon. Lysne and Clark (2009) found it in the Bruneau River (survey area from Snake River confluence upstream to Hot Creek- 41 km) in Idaho. This species was not encountered in recent surveys of Montana (Gangloff and Gustafson, 2000) but there are historical records in the upper Columbia River watershed in western Montana (perhaps the Clark Fork River or Kootenai River) (Nedeau et al., 2005). In Canada, it is found in the Columbia River system in southern British Columbia and known only from the main water bodies (Kootenay, Columbia, and Okanagan Rivers) from Penticton south to the border but only the Okanagan recently (COSEWIC, 2003; Metcalfe-Smith and Cudmore-Vokey, 2004). British Columbia distribution includes the Columbia River system with recent specimens collected from Park Rill Creek (Okanagan River tributary), Shaha Lake, and Vaseux Lake (both Okanagan system); with earlier or historic collections from Osoyoos Lake, and Okanagan Lake (all Okanagan drainage) (COSEWIC, 2003) and Okanagan River and Falls (Scudder, 1996).
