Costa Rica · Eastern Pacific

Cocos Island

Green-season window is favored for schooling hammerheads and large pelagics.

Cocos Island sits 550km off the Pacific coast of Costa Rica — a rainforested rock surrounded by deep water and one of the planet's great shark aggregations. Schooling scalloped hammerheads, Galápagos sharks, silkies, tigers (occasional), tuna, marbled rays and resident dolphins. Liveaboard-only, with a 30–36 hour crossing each way.

Good season

Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec

Year-round, but June–November (rainy season) delivers the largest hammerhead schools and worst surface conditions. December–May is calmer with clearer water and more whale sharks.

Trip duration

10–12 night liveaboard, including 2 days of transit each way.

Dive style

Negative entries into strong current, reef hooks, blue-water safety stops. Big-animal diving, deep cleaning stations.

Dive level

Advanced + 50+ dives is operator-required; nitrox certification strongly recommended.

Reef health

What you’ll actually find
At risk now

This reef is under heat stress right now and has thinned over the last decade. Plan a trip this year rather than next.

Coral reef health

How is this calculated?
A decade ago
Survey 2014
32%
Today
Survey 2024
27%

On current trend, no live coral by ~2078. Losing about 0.5% cover per year — roughly 54 years of reef left to see if nothing changes.

Heat stress right now

Alert level 1

Bleaching likely. Some coral mortality typically follows.

NOAA Coral Reef Watch · updated May 2026 · 6 °C-week heat dose

What to expect on a dive

Hammerhead schools, tigers, silvertips. Reef itself is sparse — the pelagic action is the entire reason to go.

Sources, methodology, and the raw numbers

Raw observed numbers

  • Coral cover: 27% (survey Sep 2024, Eastern Tropical Pacific reef survey)
  • Bleached: 12%
  • Recent mortality: 4%
  • Eastern Tropical Pacific — observed condition reflects the thinning regional pattern.

Raw thermal numbers

  • NOAA CRW alert level: Alert level 1
  • Degree Heating Weeks: 6 °C-wk
  • SST anomaly: +1.9 °C

How we summarise this

Observed coral cover, bleaching, and mortality come from named in-situ surveys with a stated date and method — they describe one snapshot of one reef and do not extrapolate to neighbouring sites. Current thermal stress is satellite-derived from NOAA Coral Reef Watch at ~5 km resolution; it indicates risk, not observed coral damage. We deliberately separate observed condition, current thermal stress, and projection — and we never publish a projection without a documented model and uncertainty.

Sources

Reef condition changes year to year. If you visit, consider supporting responsible-travel and conservation operators on the ground.

Pressure on this reef

Protection · fishing · what you can do

Protected-area status

No-take reserve

Fully no-take — no fishing of any kind. The strongest protection tier.

Fishing pressure

Moderate fishing pressure

Dominant pressures

  • industrial fishing on EEZ edges
  • liveaboard tourism

2 Green Fins-verified operators known at this location.

What you can do

Cocos Island National Park is no-take; illegal longline fishing on EEZ edges is the persistent threat. Support operators that fund anti-poaching patrols.

Protection status sourced from Protected Planet / WDPA and refined with Marine Protection Atlas. Fishing pressure proxy is Global Fishing Watch AIS data. See the methodology for what these sources can and can’t prove.

Dive sites here

4 curated

Gear

What to bring

Basic kit

Site-specific add-ons

Some dive sites here call for extra gear. Check the individual site page for full context.

  • Temperate-grade wetsuitThermocline drops to 19°C at depth even in season. · Bajo Alcyone
  • Reef hookStandard procedure: hook in at the up-current edge of the seamount. · Bajo Alcyone
  • Nitrox certificationMost operators run nitrox for the long deep profiles required at 25–40 m. · Bajo Alcyone
  • SMB and reelSurface intervals happen well offshore of the main island and current can push you away from the pinnacles fast — every diver carries their own marker. · Dirty Rock (Roca Sucia)

What divers say

Two days at sea, then four days of the heaviest shark traffic I've ever seen, then two days back. Worth every hour.
Photographer