The Comal Springs Riffle Beetle (Heterelmis comalensis, Elmidae) is a flightless species endemic to two springs flowing from the Edwards Aquifer in central Texas. Its primary population is in Comal Springs with a smaller population in San Marcos Springs. It was listed as federally endangered in 1997 primarily due to the threat of over-extraction of water from the aquifer. The listing led to the initiation of a research program that has improved our understanding of the species’ biology and the establishment of reproducing captive populations. Despite these advances, little definitive was known about the species responses environmental factors in the wild. The populations of H. comalensis and a co-occurring species, but non-spring-endemic species, Microcylloepus pusillus, have been monitored semiannually using cotton lures since 2004. In 2023, a more spatially expansive temporally intensive one-year population assessment was initiated to assess the distribution of H. comalensis, determine what environmental covariates relate to their abundance, and develop relative abundance estimates that can inform biomonitoring. The population study indicated that springflow was the primary driver of adult and larval H. comalensis populations, with lower springflows leading to lower populations. No other environmental covariates had clear relationships with H. comalensis abundance or habitat occupancy, although biofilm abundance on lures (a food resource) had a smaller positive effect. This contrasts with M. pusillus, which was not affected by springflow or biofilm, emphasizing the importance of maintaining springflow through droughts to support H. comalensis populations. Model results have been adapted into a framework for an annual assessment of populations using biomonitoring data. Initial analysis of long-term monitoring data suggests that abundances of both species have declined across most subpopulations in excess of what is explained by known covariates.