Whether active or passive, dispersal accompanied by gene flow shapes the genetic makeup of populations and ultimately the evolutionary divergence of species. Our objective was to determine if 2 very different aquatic invertebrates with overlapping distributions show similar dispersal histories in their phylogeographic patterns and genetic uniqueness. Two spring-dwelling invertebrates, Hyalella azteca and Callibaetis americanus, were collected from 6 adjacent closed basins in the Great Basin of western North America. Cytochrome c oxidase subunit I (COI) and the 28S ribosomal subunit were used as genetic markers in Hyalella, and COI with the 16S ribosomal subunit of the mitochondrial genome were examined in Callibaetis. Maximum parsimony (MP) and likelihood (ML) analyses, F_ST values, analysis of molecular variance (AMOVA), Mantel tests, and nested clade phylogeographical analysis (NCPA) were used to evaluate geographical associations. Hyalella azteca appears to have been in the adjacent basins much longer than has Callibaetis. F_ST values in H. azteca reached near fixation. Callibaetis americanus F_ST values were lower suggesting greater gene flow and, consequently, higher dispersal rates. Mantel tests did not detect significant isolation by distance for either species, but NCPA on smaller networks of closely related haplotypes found the genetic structure in C. americanus dominated by restricted gene flow with isolation by distance. Hyalella azteca was characterized more by gradual range expansion followed by fragmentation. These results suggest that these isolated freshwater communities are amalgams of species that entered at different times, with weak dispersers having greater constraints on movement and, thus, reflecting an older geographical story than do species with stronger dispersal capabilities.