Thailand · Andaman Sea
Richelieu Rock
Peak pelagic and whale shark timing usually falls in the open-park season.
Richelieu Rock is a horseshoe-shaped pinnacle in the Andaman Sea that rises just to the surface — a single seamount draped in purple soft coral with whale sharks, barracuda schools, frogfish, and an extraordinary macro layer. Jacques Cousteau called it one of the world's top ten dives.
Good season
October to mid-May only (Similan Marine Park is closed in monsoon). February–April is peak for whale sharks.
Trip duration
Day-trip from Khao Lak (long day) or 4–6 night Similan liveaboard.
Dive style
Multiple loops around the pinnacle; moderate current possible.
Dive level
Advanced Open Water recommended for the current and depth.
Reef health
What you’ll actually findSome loss since the 2010s, but the reef still has plenty to dive. Pick depth and shoulder-season carefully.
Coral reef health
How is this calculated?On current trend, no live coral by ~2144. Losing about 0.3% cover per year — roughly 120 years of reef left to see if nothing changes.
Heat stress right now
Mild warmth. Worth watching — no bleaching yet.
NOAA Coral Reef Watch · updated May 2026 · 5.2 °C-week heat dose
What to expect on a dive
Pinnacle dive — fish life and macro, not extensive coral. Whale-shark season Feb–Apr is the highlight.
Sources, methodology, and the raw numbers
Raw observed numbers
- Coral cover: 36% (survey Sep 2024, GCRMN / DMCR Andaman Sea transect)
- Bleached: 9%
- Recent mortality: 3%
- Andaman Sea — observed condition reflects the slow loss regional pattern.
Raw thermal numbers
- NOAA CRW alert level: Watch
- Degree Heating Weeks: 5.2 °C-wk
- SST anomaly: +0.5 °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
- Global Coral Reef Monitoring Network — GCRMN / ICRI
- NOAA Coral Reef Watch — U.S. National Oceanic and Atmospheric Administration
- AIMS Long-Term Monitoring Program — Australian Institute of Marine Science
- 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
- International Coral Reef Initiative — ICRI Secretariat
- 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
Strict MPAInside a strict marine protected area with active enforcement.
Fishing pressure
Moderate fishing pressureDominant pressures
- tourism overcapacity
- warming
- anchor damage
3 Green Fins-verified operators known at this location.
What you can do
Similan / Surin national parks close seasonally to allow reef recovery. Liveaboards only. Choose operators that respect closures.
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.
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Gear
What to bringWhat divers say
“Richelieu in March with a whale shark sliding around the rock — I've chased that dive every year since.”