The primary objective of this article is to report the co-occurrence of Spongilla lacustris (Linnaeus 1759) and Ephydatia muelleri (Lieberkühn 1855) in an alpine Colorado lake whose altitude of 3580 m represents new elevation maximums for these sponges for Colorado and for the whole of North America. A secondary objective was to characterize the physicochemical conditions of the lake water. For many limnological parameters, heavy metals, and metalloids, new minimums are recorded, particularly for E. muelleri. Ecomorphic variation of atypical gemmuloscleres for E. muelleri and S. lacustris is documented with SEM micrographs. Even though all the encrusted “white colonies” of both species were <23 mm in maximum dimension, each contained mature gemmules. The presence of both species in an ultraoligotrophic lentic site indicates the sponges' ability to colonize and persist in cold, pristine, low-solute habitats.