Aquatic vegetation was surveyed at Mammoth Spring, AR, representing the first extensive survey of this resource since 1859. Thirty-eight angiosperm species were identified during this study, including 17 species of monocots and 21 species of eudicots. Seven species were nonnative, but they are not considered invasive. Eleven of the species reported from the spring in 1859 are still present, but some previously reported taxa were not found and other taxa are reported for the first time. Species no longer found at the spring may be due to misidentifications in the earlier study or extirpations due to climate change, anthropogenic disturbances, or unknown factors. The diversity of aquatic plants in Mammoth Spring is similar to that reported from other regional large springs and a few species are shared in common among these springs.