Banco Chinchorro

Thirty kilometres off the Costa Maya lies Banco Chinchorro, one of the largest coral atolls in the Caribbean, a ring of reef about 40 by 16 kilometres enclosing a turquoise lagoon, protected as a biosphere reserve and famously fatal to shipping. Centuries of hulls met its windward wall - Spanish galleons through twentieth-century freighters - and their remains, from anchor gardens and cannon to the photogenic rusting bulk of a stranded cargo ship, make the atoll a well-known wreck-diving site. The living reef is the bigger draw: with no rivers, little runoff and almost no people, visibility can reach forty metres over coral in better condition than on most of the mainland coast - forests of elkhorn, walls of barrel sponges, clouds of grunts, reef sharks on patrol and lagoon flats where American crocodiles cruise the mangrove keys, visited with specialist operators. A handful of fishermen's stilt huts on Cayo Centro - palafitos standing over the shallows - shelter the cooperative lobstermen and the rare overnight trips. Crossings are over open sea and depend on the weather.

What's there

• The wrecks - centuries of ships on the windward wall.
• The untouched reef - elkhorn stands and forty-metre visibility.
• The stilt huts - lobster cooperative palafitos on the keys.
• The crocodile flats - specialist encounters in the lagoon.

When to go

April to August for the calmest seas and reliable crossings; winter northers cancel freely. Book with the few licensed Mahahual and Xcalak operators days ahead.

What to expect

The crossing is long, open and sometimes rough - this is an expedition day, not a beach trip. Costs reflect fuel and permits. Day trips see a fraction of the atoll; divers get the headline sites.

Nearby

Mahahual's malecon and Xcalak's village are the gateways; Bacalar's lagoon rounds out the far-south circuit ashore.

Key facts