Ferrissia californica (Rowell, 1863), an aquatic pulmonate [formerly widely known as Ferrisia fragilis (Tryon, 1863), is reported herein to have established a population in the Tskhal-Tsiteli, or Iazoni, Cave (Caucasus, Georgia), within the invasive range of this species. This is the first record of a sustained population of an invasive freshwater pulmonate in an underground environment. Possible consequences of this invasion are briefly discussed. It is possible that this alien snail may threaten the native snail species Motsametia borutzkii (Zhadin, 1932), which is endemic to Tskhal-Tsiteli Cave.