Behaviors in relation with water are described in detail for wild chimpanzees of the Mahale Mountains, Tanzania: drinking, wading streams, feeding, responses to rain, etc. When the results are compared with those of Gombe National Park, some behavioral differences emerge: drinking directly from the lake, feeding on aquatic plants, back/shoulder rubbing behavior by making day-beds, etc. are observed only for chimpanzees of the Mahale Mountains, while sponging to obtain water is observed only for those of Gombe. These may be examples of ‘tradition drift’ in wild chimpanzees. Moreover, it is suggested that there is no innate hydrophobia among any of the African great a