The Edwards Aquifer contains numerous intermittent and perennial springs throughout that are home to several species of solely aquatic, perennibranchiate (“always gilled”) Eurycea salamanders. Two of these species have two of the smallest known ranges of any vertebrate species, residing only in the complex of springs known as Barton Springs. Eurycea sosorum, the Barton Springs Salamander, inhabits the surface and immediate subsurface habitat (epigean) of Parthenia Spring (in Barton Springs Pool), Eliza Spring, Sunken Garden, and Upper Barton Spring. Eurycea waterlooensis, the Austin Blind Salamander, inhabits the deeper subterranean habitat beneath the surface of Parthenia, Eliza, and Sunken Garden. Both species require clean, cool, flowing, spring water to thrive; they are stream salamanders, not pond salamanders. The small range sizes, threats to quantity and quality of water emanating from the Barton Springs complex, and harm imposed by cleaning and maintenance of Barton Springs Pool are the main reasons E. sosorum was added to the federal list of endangered species in 1997, and E. waterlooensis was added to the list of candidate species in 2002.