The common hydrological classification for mangroves developed by Watson [Watson, J.G., 1928. Mangrove forests of the Malay Peninsula. Malayan Forest Records No. 6. Forest Department, Federated Malay States, Kuala Lumpur] is not sufficient in mangrove areas with an irregular tidal regime and elevation, such as Can Gio in Vietnam. Incorporating more detailed hydrological information in the Watson classification gave promising results for the measuring sites in Can Gio, but should be tested in other mangrove areas.