A new species of Hydrocanthus Say, 1823 is described and illustrated, H. zimmermanni sp. nov. from Peru. A distinct pattern of prosternum and prosternal process setation and aedeagal features differentiate the new species from all other members of Hydrocanthus. Two new synonyms are established: H. rubiginosus Guignot, 1942 as junior synonym of H. debilis Sharp, 1882 (syn. nov.) and H. paludimonstrus Miller, 2001 as junior synonym of H. paraguayensis Zimmermann, 1928 (syn. nov.). In addition, a key to Brazilian species of Hydrocanthus is provided.
Keywords: Coleoptera, Noterinae, burrowing water beetles, taxonomy, Neotropical Region.