Pemba Island

Diving here runs on the tide table rather than the clock. Boats leave the lodge beaches on the west coast when the exchange is right, so a briefing can be at first light one day and mid-morning the next, and the plan can still change on the water if the flow arrives early. Each lodge tends to work the gaps nearest it, so crossings are usually short and groups stay small, since only a few operators are based on the island. Two dives before lunch and something shallower in the afternoon is the usual shape of a day.

The sites are not variations on one theme. A gap dive starts at a break between an offshore islet and the fringing reef, entered up-current, flown along the drop-off face and finished mid-blue on a marker buoy. Between the gaps that same reef edge can be dived slowly, hanging under overhangs to pick out soft coral and small animals. Behind it are sheltered hard-coral shelves with almost no flow, and offshore pinnacles that need settled weather and a longer crossing to reach.

It suits divers already comfortable in moving water: descending into blue onto a reef edge, holding trim as the flow speeds up in the narrows, deploying a marker from mid-water and being collected well downstream of where the dive began. There is no shore diving and no walk-in fallback when the wind is up, so most people commit to one west-coast lodge and dive from it daily. Anyone still building buoyancy is better served on the protected inshore reefs or on Zanzibar.