We monitored Roswell springsnail (Pyrgulopsis roswellensis), Koster's springsnail (Juturnia kosteri), and Noel's amphipod (Gammarus desperatus), three endangered aquatic invertebrates, from 2014 through 2017 at Bitter Lake National Wildlife Refuge, Chaves County, New Mexico. We initiated the effort to develop baseline abundance estimates in a rigorous, repeatable framework, and to inform long-term monitoring efforts. Surveys were focused on three spring systems. Density estimates for the two species of springsnails combined ranged from 7870 ± 1693 SE snails per m² (CV = 22%) to 39,704 ± 10,035 SE snails per m² (CV = 25%) in the three systems combined. Noel's amphipod density estimates ranged from 144 ± 42 SE individuals per m² (CV = 29%) to 404 ± 109 SE individuals per m² (CV = 27%). We can detect a proportional change (α = 0.1, power = 0.8) in density ranging from 30% to 60% in Bitter Creek, Sago Springs, and the Snail Unit. We predicted increases in statistical power that could be gained from increases in survey effort. Because of seasonal changes in density in some systems, year-to-year evaluation of trends must be focused on a given season. Likewise, seasonal changes in spring flows may impact density estimates. We provide estimates of density, precision, and power that can inform future efforts to monitor both species status and restoration efforts.