Recent survey work conducted from 1994 to 2003, limits the known range of Newcomb's snail to small sites located in a total of six watersheds in north- and east-facing drainages on Kauaʻi. They are: Kalalau Stream, Lumaha`i River, Hanalei River (four subpopulations), Keālia Stream, Makaleha Stream (two subpopulations), and the North Fork Wailua River. The term "subpopulation" refers to a discreet group of individuals, separated from other discrete groups within a single watershed. Because of low mobility, no interaction between subpopulations exists. No historical information is available on the population sizes of Newcomb's snail. However, anecdotal reports indicate the Kalalau Stream and Lumaha`i River populations of Newcomb's snails are larger in comparison to the other four.