Zanzibar tides: why the east coast empties twice a day

What is actually happening

Zanzibar sits on a wide, shallow continental shelf fringed by coral reef. On the east coast the reef sits a kilometre or more offshore, and between reef and beach lies a flat lagoon barely a metre deep at high water. The Indian Ocean tidal range here reaches around three metres at spring tides.

When three metres of range meets a lagoon a metre deep and almost flat, the water does not drop — it leaves. At low spring tide the sea can be four or five hundred metres out, exposing seagrass beds, starfish, urchins and the seaweed plots that coastal women farm.

How to plan around it

The tide moves forward by about fifty minutes each day, so a week in one place gives you every combination. High tide at breakfast on Monday is high tide at lunch by Thursday.

• Check a Zanzibar tide table before you book activities. Most hotels post the day’s times at reception.
• Book boat trips, snorkelling and dhow sunsets for high water — boats cannot launch over the flats at low tide.
• Walk the flats at low tide rather than resenting them. It is the best rock-pooling on the island and the light on the wet sand at sunrise is extraordinary.
• Bring reef shoes. Urchins and sharp coral rubble are the main injury we see.
• Every decent east-coast hotel has a pool for the hours the sea is gone. Check that yours does.

The seaweed farms

The green and red plots staked out across the east-coast flats are seaweed farms, worked almost entirely by women, and for decades one of the few independent incomes available in coastal villages. Warming sea temperatures have hurt the crop badly in the last ten years. Several villages now run tours of the farms and small workshops turning seaweed into soap and oil — a direct and worthwhile place to spend money.