Trichomycetes are a group of fungi and protists living in the guts of immature aquatic insects and other arthropods. The nature of this relationship is poorly understood but it is mostly described as obligately commensalistic, with the microbes exploiting a unique microhabitat. Collections of trichomycetes were made from freshwater insects in aquatic habitats near Castlegar in the Columbia Mountains, part of the Rocky Mountain Range in southeastern British Columbia. The collection sites were at altitudes ranging from 435 to 935 m and were made in July 2006. A total of 32 species were recorded including four new species, Harpella filispora sp. nov., Orphella columbiensis sp. nov., Smittium nodiradicatum sp. nov., and Smitium basiangustatum sp. nov. described here. These are the first records from Western Canada and two, Austrosmittium patagonicum and Glotzia distorta are new continental records. These findings are compared to reports from the western edge of the Rocky Mountain range near the Boise Mountains in Idaho and the Southern Rockies in Colorado.