Tikehau

Everything runs off the tide table. Boats leave from the village on the atoll's southwestern rim and run up the western side to the pass, so the day is built backwards from the moment the flood starts pushing water in rather than from a fixed departure time. Centres run a two-tank morning, and if the timing is wrong the pass is left alone and the boat works closer sites instead. Afternoons are usually free, which is why most people pair diving with trips out to the pink-sand motu and the bird islet.

Three environments sit within a short boat ride of each other and they dive nothing alike. The ocean side is a proper drop-off, taken in blue with the reef on one shoulder and nothing on the other. The channel is a hard-bottomed groove with a shallow plateau at its mouth, where the reef fish gather and the water moves hardest. Inside, the lagoon flattens into sand with coral heads standing on it, calm enough that a dive there is mostly hovering and waiting for something to come to you.

The signature dive is a one-way trip. You go in outside on the incoming water, work down to the mouth, hold on the plateau in the shelter of the coral while the flow runs past, then let go and ride the channel through into the lagoon, finishing shallow over coral heads while the boat tracks your bubbles. Groups go in fast and descend together, because the drop point matters more than a tidy entry, and anyone slow to clear their ears is pushed off the site before reaching the bottom.

It suits divers who have drifted before and are content to spend a week on one pass in its different moods instead of ticking off a long site list. Operator numbers are small and there is usually little competition for a site, which is the trade against the busier Tuamotu atolls. Air Tahiti's inter-atoll hops make it straightforward to string two or three of them into a single trip, and this tends to be the quieter stop in that sequence.