Cozumel

The pattern is a two-tank morning boat and very little else to arrange. Crews run south, dive the deeper site first, break for an hour on the water, then finish shallower and closer to town. Nobody ties up: divers roll in together and the boat follows the bubbles, collecting everyone wherever they surface. Afternoon single-tank trips and night dives leave from the same marinas, and a national marine park fee is charged on top of the trip, usually collected by the operator.

The reefs run in a line down the sheltered west side of the island, and the grooves between the coral buttresses do more than break the reef up: they funnel the flow and set the line of the dive. The buttresses themselves are undercut and tunnelled, so time goes on slipping in and out of gaps rather than following a reef edge. Sites grow deeper, taller and more carved the further south the boat runs; the northern reefs are shallower, the flow across them gentler, and being nearest the marinas they take the short afternoon trips.

Current strength is the day's main variable, and it is rarely known until the boat is over the site. On a fast day one tank covers a long stretch of reef; on a slow one a group can work the same set of canyons properly, which is when the small residents under the ledges get found. Conditions are least dependable from August through November, and even in the calm early-year months a northerly blow can shut the port for a day, so leave slack rather than booking a tight connection home.

It suits divers who can hold trim without fighting the water; buoyancy counts for more here than a logged depth. The shallower northern reefs are where less experienced divers usually start, with a guide setting the pace. It works less well for anyone who wants to park on a subject for twenty minutes: the wall and drift sites are boat-only, though a handful of shore entries along the hotel strip cover checkout dives, macro and night dives. Many people pair the island with the mainland cenotes, a ferry crossing and a drive up the coast away.