Eurycea rathbuni is a troglobite: pigmentless, with eyes reduced to dark spots beneath the skin, retaining external gills for life because it never leaves water. It is known from a small number of sites near San Marcos, including Ezell's Cave and artesian wells, all drawing on the same aquifer system.
Because the animal lives in inaccessible flooded voids, most encounters are incidental, with individuals flushed out at spring openings. Its food arrives from above, in the form of invertebrates carried in with recharge water; it hunts by detecting water movement rather than by sight. Population size cannot be counted directly and is estimated indirectly.
The salamander's status is inseparable from the aquifer's. Anything that lowers water levels or degrades recharge water quality reaches it immediately, because there is no alternative habitat to retreat to. It is listed as endangered under the US Endangered Species Act, and a captive assurance population is maintained.