Because of its geological uplift, Rurutu has almost no lagoon and its waters are very shallow (164 feet / 50 m). It is thus possible to observe the whales swimming around the island within 328 feet (100 m) of the coasts and to see them from the surface even when they are on the ocean floor. Furthermore, the central north-south mountain, protecting alternately the east and the west coasts, allows navigation in spite of the polar depressions of the austral winter.