Cocos Island Liveaboard Diving: Bajo Alcyone, Dirty Rock and Manuelita

Isla del Coco sits about 550 km southwest of the Costa Rican mainland, alone in the eastern tropical Pacific. It is a national park, a UNESCO World Heritage Site since 1997, and one of the few places where the sheer number of scalloped hammerheads is the reason people cross an ocean. Nobody lives on the island apart from park rangers. There is no airstrip, no hotel and no dive shop: every diver arrives on a liveaboard after a crossing of roughly 36 hours from Puntarenas.

The diving happens on submerged pinnacles and seamounts that rise from deep water within a few hundred meters of the coast. Currents carrying nutrients from the deep bring the pelagics close: hammerheads gather on cleaning stations at 25 to 35 m, Galapagos and silky sharks patrol the blue above, and marbled rays rest on the ledges. In the rainy season, roughly June to December, the schools are at their largest and whale sharks pass through.

What a Cocos trip looks like

A typical itinerary lasts 10 to 11 days door to door, with seven full days of diving at the island, usually three dives a day plus the occasional night dive at Manuelita. Boats anchor in Chatham Bay or Wafer Bay and run skiffs to the sites. Most dives are 30 to 45 minutes of holding on to rock at depth watching sharks, followed by a drift into the blue for the safety stop. Between dives there are ranger-guided walks to the waterfalls, the only time you set foot on land.

This is not a destination for the newly certified. Operators generally ask for Advanced Open Water plus a meaningful logbook, because depth, current and surge are the norm rather than the exception. Nitrox is standard on the boats and makes the repetitive 30 m profiles far more comfortable. For divers who are ready, Cocos delivers a density of large animals that few places match on a consistent basis.

Cocos rewards divers who want big animals in numbers and are prepared to work for them. The island is isolated enough that only a handful of liveaboards operate there, so sites are rarely shared with another group.

• Hammerhead schools: scalloped hammerheads gather in schools that can number in the hundreds on the seamounts, particularly Bajo Alcyone and Dirty Rock, and they are reliable in season from June to December.
• Shark variety: Galapagos, silky, silvertip, blacktip and whitetip reef sharks are all frequently seen on the same trip, and tiger sharks have become regular visitors since the early 2010s.
• The Manuelita night dive: dozens of whitetip reef sharks hunting in packs across the coral garden by torchlight, one of the more intense night dives anywhere.
• Whale sharks and rays: whale sharks pass through most often between June and September, and marbled rays, eagle rays and mobulas are common on the ledges and in the blue.
• Genuine remoteness: no day boats, no resorts and no other traffic, just your boat, the rangers and the island.
• Ranger-guided hikes: short walks to waterfalls and the historic carvings at Chatham Bay give a rare look at a rainforest island that has never been settled.

Around twenty sites are dived regularly, almost all within a short skiff ride of the two anchorages. Most are pinnacles and seamounts where the plan is the same: descend quickly, find a spot on the rock at 25 to 35 m, and wait while the hammerheads come to the cleaning stations. The sites below are the ones that anchor nearly every itinerary.

Bajo Alcyone (east coast)

A seamount whose summit sits at about 25 to 28 m, named after Jacques Cousteau's ship. This is the classic hammerhead site: divers settle on the top of the mount and watch schools of scalloped hammerheads circle the cleaning stations, often with Galapagos sharks and big schools of jacks above. Current can be strong and the dive is short by design, so nitrox helps.

Dirty Rock (north coast)

A cluster of rocks and pinnacles separated by a channel, and probably the most productive single site on the island. Hammerheads pass through the channel in numbers, marbled rays rest on the sand at the base, and huge schools of bigeye jacks and snappers fill the water column. Whale sharks and tiger sharks turn up here regularly in the rainy season.

Manuelita (northeast, off Chatham Bay)

The small island just outside Chatham Bay offers two very different dives. Manuelita Outside is a deep wall and boulder slope with hammerheads and Galapagos sharks in the current. Manuelita Coral Garden, on the sheltered side, is shallow and is the site of the famous night dive, when whitetip reef sharks hunt in packs among the coral heads.

Dos Amigos Grande (southwest)

Two rock islets on the exposed side of the island. The larger one has a swim-through arch at around 25 m that hammerheads and eagle rays pass through, and the surrounding walls hold whitetips and marbled rays. Surge and current make this an advanced dive, usually saved for calmer days.

Punta Maria (west coast)

A deep pinnacle whose top lies around 25 to 30 m, with a cleaning station that draws hammerheads and a steady presence of Galapagos sharks. The site is further from the anchorages and more exposed, so it is dived when conditions allow, and it is often the quietest and most rewarding hammerhead dive of the week.

Submerged Rock (north coast)

A pinnacle that rises to about 5 m below the surface with a tunnel running through its base. Whitetip reef sharks pack the tunnel, marbled rays sit on the ledges, and hammerheads and eagle rays cruise the outer walls. Visibility here is often the best on the island.

Cocos is a pelagic destination first. The seamounts are cleaning stations and feeding grounds for sharks and rays drawn in from the open Pacific, and the volume of fish in the water column is remarkable even by Pacific standards. Reef life is present but secondary, and macro diving is not why people come.

Pelagics

• Scalloped hammerheads in schools, reliably from June to December and present year-round in smaller numbers.
• Galapagos, silky, silvertip and blacktip sharks, with tiger sharks now frequently seen at Dirty Rock and Manuelita.
• Whale sharks, most often between June and September, and occasional mobula rays.
• Marbled rays, spotted eagle rays and bottlenose dolphins, plus yellowfin tuna and wahoo in the blue.
• Bigeye jacks, snappers and horse-eye jacks in schools dense enough to block the light.

Reef

• Whitetip reef sharks in large numbers, particularly hunting at night in the Manuelita coral garden.
• Green turtles, hawksbills, large green morays and octopus on the boulder slopes.
• The rosy-lipped batfish, a Cocos endemic, sitting on sand patches at depth.

Macro

• Limited by the nature of the sites, but frogfish, nudibranchs and cleaner shrimp are found in the shallows around Chatham and Wafer Bay.

Cocos is exposed open-ocean diving. Currents on the seamounts range from moderate to strong and can change direction mid-dive, surge is common on the shallower pinnacles, and descents are often made hand over hand along a line. Divers are expected to carry a surface marker buoy and be comfortable with negative entries and drifting safety stops in the blue.

Water temperature at the surface is 24 to 28 C for most of the year, but thermoclines at 20 to 30 m can drop the temperature to 20 to 22 C, particularly in the rainy season. A 5 mm suit with a hood is the usual choice, and many divers prefer a 7 mm or a semi-dry from July to November. Visibility averages 15 to 30 m; it is better in the dry season and lower in the plankton-rich months, which is precisely when the hammerhead numbers peak.

Most dives are between 25 and 35 m, with three dives a day for seven days. Operators typically require Advanced Open Water and a logbook of at least 50 dives, some more, and nitrox is strongly recommended for the repetitive deep profiles.

Cocos can be dived year-round, but the two seasons offer quite different trips. The rainy season, from roughly June to December, brings cooler, plankton-rich water, rougher crossings and the largest concentrations of hammerheads and whale sharks. The dry season, from December to May, offers calmer seas and better visibility with fewer, though still present, sharks.

• June to September: the peak hammerhead months, with schools at their largest and whale sharks passing through. Expect lower visibility, thermoclines and swell on the crossing.
• October to December: hammerhead numbers remain high, tiger sharks are frequently seen, and the weather starts to settle towards the end of the year.
• January to March: the calmest seas and clearest water, with warmer temperatures and comfortable crossings. Hammerheads are still present in smaller groups, and Galapagos sharks and rays are reliable.
• April to May: the transition months, warm water and generally good visibility, with shark numbers building again as the rains return.

All Cocos Island trips depart from Puntarenas on the Pacific coast of Costa Rica, and the only way to reach the island is on a liveaboard. There is no airstrip on the island and no other transport.

Fly into Juan Santamaria International Airport (SJO) in San Jose, which has direct connections from the United States, Canada, Mexico, Panama and several European cities including Madrid, Frankfurt, Amsterdam, Paris and London. Liberia (LIR) in the northwest is an alternative, but the road transfer to Puntarenas is longer. From San Jose the drive to Puntarenas takes about two hours on the Route 27 highway, and most operators include this transfer, with a pickup from a San Jose hotel on the morning of departure.

The crossing from Puntarenas to the island takes approximately 36 hours in each direction, so a 10-day trip typically gives seven days of diving. The open Pacific can be rough, especially between June and November; seasickness medication is worth packing even for divers who rarely need it. Plan to arrive in San Jose at least one night before departure and to leave no earlier than the day after the boat returns.

Citizens of most European countries, the United States, Canada, Australia and many others do not need a visa for tourist stays of up to 180 days; check the current rules for your passport before booking.

Cocos Island National Park charges a daily fee for every diver, approximately USD 70 per person per day at the island, which most liveaboards bill separately from the trip price; expect roughly USD 490 to 590 for a seven-day stay and confirm the current amount with the operator. Park permits are handled by the boat.

Costa Rica uses the colon (CRC), but US dollars are accepted almost everywhere and most boats settle onboard extras in dollars by card or cash. Plugs are type A and B at 120 V. Spanish is the official language and English is widely spoken in tourism.

Nitrox is available on the boats currently operating and is usually included or offered for a small supplement; some vessels support rebreather divers with sorb and oxygen on request. There is no hyperbaric chamber on the island, so dive accident insurance is compulsory with every operator, and general travel insurance with evacuation cover is strongly advised.

• Log some current dives first: Cocos is not the place to discover you dislike holding on to a rock in a 2-knot current at 30 m. Build experience in Komodo, the Red Sea or Palau beforehand.
• Bring gloves and a reef hook: the rock is volcanic and sharp, and most sites are dived from a fixed position. Gloves are expected, not frowned upon.
• Pack for the crossing: 36 hours each way in open ocean is long. Seasickness tablets, a book and a charged tablet make a difference.
• Take the thermocline seriously: surface water may read 27 C while the cleaning station is at 21 C. A hood and a thicker suit keep you on the rock longer.
• Dive nitrox: three dives a day at 30 m for a week adds up. Nitrox extends bottom time on the mount and shortens the gap between dives.
• Do not chase the sharks: hammerheads are shy. Stay low, breathe slowly and let them come to the cleaning station; groups that swim at them empty the site for everyone.
• Join the hikes: the ranger-led walks to the waterfalls are short and the island is one of the least visited rainforests on earth.