Part of the Montana State Library collection. Prepared for: USDA Forest Service Northern Region "May 2007." Using prior published reports, the MT Natural Heritage Program Species of Concern list, the Idaho Comprehensive Wildlife Conservation Strategy (CWCS) and the NatureServe Explorer database as starting points, we compiled a list of 33 aquatic macroinvertebrate species likely to occur within the U.S. Forest Service Northern Region that were ranked as G1-G3 or T1-T3 in 2006, thereby meeting USFS Species of Concern (SOC) criteria, and one mussel taxon ranked Tier I in the MT CFWSCS, thereby meeting USFS Species of Interest (SOI) criteria. Subsequent to evaluating habitat and occurrence data, many of these aquatic invertebrate taxa proved to be peripheral to USFS Northern Region lands and thus, would be of little value to future management plans. Therefore, we pared the initial SOC list down to 19 species and increased the SOI list to 27 species by adding 12 SOI from the Idaho CWCS and another 15 previously considered by MTNHP. The number of documented aquatic invertebrate SOC species distributed on the Region 1 Forests were as follows: in MT, Beaverhead-Deerlodge (4), Bitterroot (5), Custer (0), Flathead (6), Gallatin (1), Helena (1), Kootenai (1), Lewis & Clark (2), Lolo (12) and in ID, Clearwater (9), Idaho Panhandle (1), Nez Perce (5), while the number of documented aquatic invertebrate SOI species is as follows: in MT, Beaverhead-Deerlodge (4), Bitterroot (4), Custer (0), Flathead (7), Gallatin (1), Helena (0), Kootenai (0), Lewis & Clark (1), Lolo (7) and in ID, Clearwater (9), Idaho Panhandle (1), Nez Perce (3) (Table 6). The patterns of aquatic SOC and SOI diversity are similar with more of these species occurring in the Lolo, Clearwater and Flathead National Forests. We documented 218 new locations for nine SOC taxa and the SOI freshwater mussel during our 2006 study. This study also documented four SOC species that are newly reported or at least re-discovered for Montana, the Lolo mayfly, Caurinella idahoensis (5 sites), the stonefly, Soliperla salish (4 sites) and the caddisflies, Rossiana montana (7 sites) and Goereilla baumanni (3 sites) all within the Lolo National Forest. A positive outcome of this study will be downgraded global ranks for at least two species (the Agapetus caddisfly, Agapetus montanus and the mayfly, Caudatella edmundsi) from G1G3 to G3. Unfortunately, this study reports the presumed extirpation of the shortface lanx, Fisherola nuttali in the state of MT due to no sightings in the past 50 years, and other extirpations of known sites reported from the literature. Furthermore, the taxonomic validity of 3 SOC Stagnicola spp (elrodi, elrodiana and montanensis) is in debate by different taxonomists, and has lead to enough ambiguity of their species status that they are no longer tracked by MTNHP or comprehensively surveyed, but their existing site locations are reported. Initial findings indicate that the number of USFS aquatic SOC increases with proximity to the Idaho-Montana border, especially within the Clearwater & Lolo National Forests which lie in the Northern Rocky Mountain Refugium (NRMR) area. The NRMR area is an important trans-border area of species endemism starting from Lookout Pass in the north to Lost Trail Pass in the south, which is an island of mountainous forest spared from the glaciers and Lake Missoula flooding to the north and lava flows from the south. In terms of habitats, the highest diversity of USFS SOC species are found in the steep-gradient headwater, forested streams (12 species), with the next most ?important? SOC habitat being moderate gradient, medium-sized, forested streams (10 species), followed by the cold mountain spring and seep habitats (6). Additional inventory in these habitats within the NRMR area would be worthwhile to fill remaining distribution gaps, to evaluate habitat associations thoroughly enough to develop predictive distribution models, and build the foundation for developing a long-term SOC monitoring and a robust aquatic management protection plan Agreement Number