Bajo Alcyone, Cocos Island

Verified2026-09-11 checkedPelagicDrift

A seamount 550 km offshore where scalloped hammerheads school in the hundreds.

Depth: 25–40 m82–131 ft
Difficulty: Technical
Entry: Liveaboard
Typical current: Extreme
Coordinates: 5°31.998′N 87°3.000′W
Activities: Scuba · Technical

Alcyone is a submerged seamount discovered by Cousteau's crew, topping out around 25 m in open Pacific. Divers descend fast, hook or hold onto rock at the summit, and watch schooling hammerheads pass overhead in numbers that are hard to credit. The current is severe, the water is cold and thermoclines are sharp, and there is nothing shallow to retreat to. Liveaboard only, and operators expect a serious logbook.

Liveaboard from Puntarenas, Costa Rica; 30 to 36 hours of crossing each way.

Best season

ExcellentJun–Nov
GoodDec
FairJan–May

Before you get in

Past 30 m, where no-stop time and gas both go quickly and nitrogen narcosis starts to show.
Recorded as a site with strong current. Settle your gas reserve, when you would call the dive, and your surface signal before you get in.
A drift dive: you do not come back to where you went in, so boat pickup and an SMB are part of the plan rather than extras.
Graded technical — it assumes equipment and procedures outside recreational training.

Taken from this site’s recorded depth, type and current, and nothing else. An empty list is not a safe site — the sea on the day, the local geography and the boat traffic are not in it. The briefing on the spot comes first.

Conditions

Water temperature: 30.4°C87°F
Wave height: 1.3 m4 ft
Air temperature: 25.6°C78°F
Wind speed: 9.5 km/h5.9 mph

Updated 2026-10-07 16:15 UTC · Source: Open-Meteo

Weather data by Open-Meteo.com (CC BY 4.0)

Conditions are reported for information only. Assess the site yourself and follow your guide and your training.

No live conditions for this site yet.

We only show numbers we can attribute to a source.

Sea state and tide

On a date

Tide · 10/7

Low05:16-0.35 m
Low17:40-0.43 m
High23:571.53 m

Forecast heights against mean sea level. Real tides in a bay, a harbour or over a flat can differ — check an official tide table before you get in.

Pick a day to see its tide

Only wave height and wind are scored, because those are what close a boat ramp or a shore entry. Water temperature is reported and never scored: 12°C is an ordinary dive in a drysuit and punishing in a 3 mm, and a number that cannot see your suit has no business marking it down. Stars do not decide whether you get in — you and your guide do, on the day.

Weather data by Open-Meteo.com (CC BY 4.0)

Marine life you may see

Scalloped hammerheadSphyrna lewiniCommon
Whitetip reef sharkTriaenodon obesusCommon
Giant oceanic manta rayMobula birostrisSeasonal
Whale sharkRhincodon typusRare
Bigeye trevallyCaranx sexfasciatusCommon
Galapagos sharkCarcharhinus galapagensisCommon
Silky sharkCarcharhinus falciformisCommon
Bottlenose dolphinTursiops truncatusSeasonal
Yellowfin tunaThunnus albacaresCommon
Olive ridley turtleLepidochelys olivaceaSeasonal
SailfishIstiophorus platypterusRare

From divers

What people who were in the water reported. Not a forecast, and not a judgement about whether the site is safe to dive.

No recent reports from divers. If you dived here in the last two weeks, you can say how it was.

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