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
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 findThis 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?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
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
- International Coral Reef Initiative — ICRI Secretariat
- NOAA Coral Reef Watch — U.S. National Oceanic and Atmospheric Administration
- AIMS Long-Term Monitoring Program — Australian Institute of Marine Science
- Global Coral Reef Monitoring Network — GCRMN / ICRI
- Atlantic and Gulf Rapid Reef Assessment — AGRRA Program / Perry Institute for Marine Science
- NOAA National Coral Reef Monitoring Program — NOAA Coral Reef Conservation Program
- Reef Check — Reef Check Foundation
- NOAA CoastWatch / OceanWatch — NOAA NESDIS / STAR
- Allen Coral Atlas — Arizona State University Center for Global Discovery and Conservation Science
- Great Barrier Reef Marine Park Authority — Australian Government
- Reef Life Survey — Reef Life Survey Foundation
- NASA PO.DAAC — NASA Jet Propulsion Laboratory / Caltech
- Copernicus Marine Service — Mercator Ocean International for the European Union
- NASA Ocean Color (OB.DAAC) — NASA Goddard Space Flight Center / Ocean Biology Processing Group
- Argo float network — International Argo Program / UCSD
- CoralWatch — University of Queensland
- IMOS / AODN — Integrated Marine Observing System / Australian Ocean Data Network
- WRI Reefs at Risk Revisited — World Resources Institute
- Ocean Health Index — OHI partnership (Conservation International + UCSB + NCEAS)
- IPCC Special Report on the Ocean and Cryosphere (SROCC) — Intergovernmental Panel on Climate Change
- GOA-ON — Global Ocean Acidification Observing Network — GOA-ON Secretariat + IOC-UNESCO
- HAEDAT — Harmful Algae Event Database — IOC-UNESCO Intergovernmental Panel on Harmful Algal Blooms
- NCEI Marine Microplastics — NOAA National Centers for Environmental Information
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 doProtected-area status
No-take reserveFully no-take — no fishing of any kind. The strongest protection tier.
Fishing pressure
Moderate fishing pressureDominant 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
Bajo Alcyone
Submerged seamount 25 m below the surface, rising from the deep. Hammerhead schools in the hundreds patrol the up-current edge. Cold thermoc…

Dirty Rock (Roca Sucia)
Cluster of jagged pinnacles off Cocos's northwest corner, streaked with guano that gives the rock its name. Drop down a wall to 20–25 m and …

Manuelita Island
A 150 m basalt islet off the north-east corner of Cocos with three named dives: a deep outside wall holding scalloped hammerhead cleaning st…

Dos Amigos Grande
The larger of two rock spires that break the surface off the exposed southwest corner of Cocos. The signature dive is the cleaning station n…
Gear
What to bringSite-specific add-ons
Some dive sites here call for extra gear. Check the individual site page for full context.
- Temperate-grade wetsuit — Thermocline drops to 19°C at depth even in season. · Bajo Alcyone
- Reef hook — Standard procedure: hook in at the up-current edge of the seamount. · Bajo Alcyone
- Nitrox certification — Most operators run nitrox for the long deep profiles required at 25–40 m. · Bajo Alcyone
- SMB and reel — Surface 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.”