The reticulated siren is one of the largest species of extant (living) salamanders worldwide, reaching up to in total length, which rivals the hellbender of the Appalachian Mountains as both the largest amphibian in North America and the third largest salamander in the world. It has a greenish grey, eel-like body, large external gills, and two small front legs. The sides and belly are a lighter yellowish green. It has an average snout to vent length (SVL) of .