Maracaibo

Entry is into swell more often than not, over a shelf of white sand inside the wall, and from there you go down fast. The top of the wall is at about twenty-seven metres1. Nothing above it is worth stopping for, so the dive starts at its deepest point and the clock starts with it. Twenty minutes is what the wall gets.

The lip you arrive at is a solid crest of coral standing three to four metres proud of the drop and leaning out over it in places, and outside it the reef keeps falling to fifty or sixty metres before the ground goes away entirely2.

The set piece is an arch. A fissure cuts across the lip; you drop into it about nine metres, come out on the face of the wall and swim north, and a roughly circular opening about nine metres across appears in the rock. You go in from underneath and swim up through it. Most groups build the dive around that one thing.

Then the profile has to come up, and there is nothing to come up onto. Everywhere else on this coast the shallow ground is where the back half of the dive happens. Here the top of the wall is the shallowest thing on the reef, so the ascent is a drift in open water with the coral somewhere off to one side and nothing at all underneath. That is where the animals are. Turtles work the face, and what divers watch the blue for is sharks and rays. The dive ends over the sand inside the wall, or by drifting shorewards onto the neighbouring reef at Chunchaka'ab, and both get used the same way: as water to let the computer come back in before the stop. Neither is a dive of its own.

Most people who dive Cozumel for a week never see this reef, and nothing about their diving is the reason. Maracaibo is gated by money and by the boat. Shops that sell it add a supplement of roughly eighteen to twenty-five US dollars a head for the fuel. Several will only go if the day fills as a private charter, which takes four to seven divers to commit. One needs permission from the harbour master before the boat leaves. Some want two dives with them first, one puts a divemaster in the water to watch you and reserves the right to decline whatever card you hold, and another asks for fifty logged dives, an Advanced card, a warm-up dive and a guide's approval on the day. One does not schedule it at all and keeps a list instead. The supplement is not an island rule either: at least one shop charges nothing extra for the far-south run, and that shop does not sell this reef at all. Plenty of others publish a full site list whose southern end is Punta Sur.

What the money buys is the one place in the park where the reef stops being something you swim along and becomes a rim you look over. Everywhere else here keeps coral on one side of you for the whole dive. On this reef the coral is a lip at twenty-seven metres with a hole cut through it, and the rest is water. The geometry is also why the marine life is different. Big sharks are not what this island is dived for, and this is the reef where hammerheads and eagle rays get named, out in the blue and well off the coral. There is no season for them and no way to plan around them. They are why divers come. The dive owes nobody a sighting. Divers who know this island well tend to rate the trip above the tunnel dive at the other end of the same run.

The name is usually traced to a headland on this coast called Punta Maracaibo, and not to the city in Venezuela. Most of the reef names on this side of the island came the same way, off ranches and landmarks on the shore behind the water: Palancar, Colombia, Paraiso, San Clemente.

Then it travelled in the other direction. That unbroken lip is not particular to this site. Reefs run the same way along the whole southern end of the island, a single calcareous parapet following the very edge of the drop, while the reefs further north are built from separate coral blocks with gaps of a few metres up to fifty between them. The southern form is known locally as arrecifes de Maracaibo, and the local usage has been part of the scientific description of Cozumel's reefs since 19912. The reef gave its name to a whole category of them.

Figures published for this reef run from about twenty-one metres to forty-nine, and the top of that spread is not something anyone should be diving on a recreational plan. The park caps sport diving at forty-five metres2, and some of the deeper descriptions in circulation belong to a decompression profile. The dive the boats sell sits between twenty-seven and thirty-seven. Have the number said out loud on the dock.

Your card runs out early here. Advanced Open Water authorises thirty metres and the wall lip is at twenty-seven, and unlike Santa Rosa Wall or Palancar Gardens there is no shallow half of this reef to dive instead if the deep part is more than you want. The training that fits is a Deep Diver specialty. Mexican law has nothing to say about any of it, because the park accredits the guide and not the diver, so the rule you will actually meet is the shop's own.

The standard island fill will not cover this one. EAN32 has a maximum operating depth of 33.8 m at a PO2 of 1.4, and the deep end of the plan sits below that. On paper a repetitive profile with nowhere shallow to offgas over is a case for enriched air, so ask what the shop can blend. The mix on the rack is not it.

A marker buoy is how the boat finds you. The whole ascent happens in open water off the most exposed corner of the island, a long way from the reef and further from the boat, and the group is what the captain is following. One number worth knowing about that group: the park allows a guide six divers in this zone and eight further north, while a charter needs four to seven before a shop will commit the day. Those two figures sit close together, so expect a full boat and not a quiet one.

Weather has the last word and nobody controls it. Big swell on entry is ordinary here and not the sign of a bad morning, and whether the corner is workable is the captain's call on the day. No month puts this dive on and no month takes it off. Leave slack in the week, and raise this dive when you book the trip.