Tuamotu Archipelago

The Tuamotu Archipelago stretches 1,500 kilometres across the central Pacific, northeast of Tahiti: 78 atolls and low islands arranged in a loose northwest-to-southeast chain. The atolls are among the lowest-lying land in the Pacific — most rise no more than 3 metres above sea level — and their existence depends on a precise balance between coral growth rates and sea level. The tidal regime throughout the Tuamotus is mixed semidiurnal, with spring ranges of approximately 0.3 to 0.6 metres in open-ocean atolls. But tidal range alone does not convey the hydrodynamic reality: the passes — the channels through which each atoll's lagoon exchanges water with the open Pacific — concentrate the tidal flow into currents of extraordinary velocity. Rangiroa's two passes, Tiputa and Avatoru, are the best-documented examples. The Rangiroa lagoon is approximately 80 kilometres long and 30 kilometres wide — one of the largest in the world. All that water floods in and drains out through two passes totalling perhaps 600 metres of combined width. At spring tides, the resulting current through Tiputa Pass reaches 6 to 8 knots. The current is so strong that the surface of the pass shows standing waves, boils, and whirlpools during peak flow. Spinner dolphins congregate at the pass mouth on the outgoing tide to surf the current and feed on fish disoriented by the turbulence. Fakarava, designated a UNESCO Biosphere Reserve, has two passes — Garuae in the north (the widest in French Polynesia) and Tumakohua in the south. The south pass is famous for the shark aggregation it supports: up to 700 grey reef sharks hold station in the pass on the incoming tide, feeding on fish swept through by the current. This is one of the largest documented shark aggregations in the world and is a scheduled dive for virtually every liveaboard visiting the Tuamotus. Both passes require timing to the current and should be dived with an operator familiar with the day's tidal schedule. Tikehau, a small circular atoll west of Fakarava, has a single pass and a lagoon famous for its clarity and its pink-sand interior beaches. The pass carries a moderate current on springs and is diveable as a gentle drift. Eagle rays and manta rays are regular visitors on the incoming tide.