Determining cryptic species and diversity in at-risk species is necessary for the understanding and conservation of biodiversity. The endangered Banff Springs Snail, Physella johnsoni, inhabits seven highly specialized thermal springs in Banff National Park, Alberta, Canada. However, it has been difficult to reconcile its species status to the much more common Physella gyrina using ecology, morphology and genetics. Here we used pooled whole-genome sequencing to characterize genomic variation and structure among five populations of P. johnsoni and three geographical proximate P. gyrina populations. By comparing over two million single nucleotide polymorphisms, we detected substantial genetic distance (pairwise F_ST of 0.27 to 0.44) between P. johnsoni and P. gyrina, indicative of unique gene pools. Genetic clusters among populations were found for both species, with up to 10% for P. johnsoni and 30% for P. gyrina of genetic variation being explained by population structure. P. johnsoni was found to have lower genetic diversity compared to P. gyrina, however, no patterns of were observed between genetic diversity and population minimums. Our results confirm that designation of P. johnsoni as an endangered species is warranted and that both P. johnsoni and P. gyrina exhibit microgeographic population genomic structure suggestive of rapid local adaptation and/or genetic drift within environments. This study showcases the utility of genomics to resolve patterns of cryptic species and diversity for effective conservation management. Future studies on the functional genomic diversity of P. johnsoni populations are needed to test for the possible role of selection within this thermal spring environment.