Belize · Caribbean
Great Blue Hole
Late spring often brings calm seas and strong visibility offshore.
The Great Blue Hole is a 124m-deep collapsed limestone sinkhole inside Lighthouse Reef — a circular sapphire stamp in the middle of the atoll. The dive itself is a bucket-list checkbox more than a marine-life experience: stalactites at 40m, a few Caribbean reef sharks circling, and a long deco-style ascent. The surrounding atoll reefs are the real diving.
Good season
April–June has the calmest seas and clearest viz. November–March can blow out the long boat ride.
Trip duration
Day-trips from Ambergris Caye or San Pedro (3–4 hours each way), or a 6–7 night Lighthouse/Turneffe liveaboard.
Dive style
One deep dive into the sinkhole (to ~40m) plus 2 reef dives on the surrounding atoll. Long boat day.
Dive level
Advanced Open Water required by most operators; deep diver specialty preferred.
Reef health
What you’ll actually findThis reef is losing coral faster than it's recovering. If it's on your list, go sooner — and manage expectations on coral colour.
Coral reef health
How is this calculated?On current trend, no live coral by ~2044. Losing about 1.1% cover per year — roughly 20 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 · 0 °C-week heat dose
What to expect on a dive
The Great Blue Hole itself is a geological dive — coral cover isn't the point. Surrounding atoll reefs are thinning.
Sources, methodology, and the raw numbers
Raw observed numbers
- Coral cover: 22% (survey Sep 2024, AGRRA reef survey protocol)
- Bleached: 20%
- Recent mortality: 8%
- Caribbean post-2023 — observed condition reflects the declining regional pattern.
Raw thermal numbers
- NOAA CRW alert level: Watch
- Degree Heating Weeks: 0 °C-wk
- SST anomaly: +1.1 °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
- Atlantic and Gulf Rapid Reef Assessment — AGRRA Program / Perry Institute for Marine Science
- 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
- 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
- sargassum influx
- SCTLD
- tourism overdevelopment
3 Green Fins-verified operators known at this location.
What you can do
The Blue Hole sits within the Belize Barrier Reef Reserve, a UNESCO World Heritage Site. Mesoamerican Reef is partially protected by national parks. Sargassum and SCTLD are the dominant pressures. Support operators participating in coral nurseries.
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.
Pollution & water-quality
What divers should knowSargassum influx
CONCERNINGSince 2018
Atlantic sargassum blooms wash onto Belizean shorelines and into the atoll. Underwater impact at the Blue Hole itself is limited.
What this means for your trip
Blue Hole proper sees little impact — it's a deep geological feature. Surrounding atoll reefs are affected. Trip-cost includes Marine Reserve fee.
Dive sites here
3 curated
Half Moon Caye Wall
Vertical wall on the eastern edge of Lighthouse Reef with massive barrel sponges, black coral, and a steady parade of eagle rays. Top of the…
Long Caye Ridge
Spur-and-groove reef along Long Caye's protected lee, with healthy hard coral cover, garden eels in the sand patches, and resident green mor…
Hol Chan Marine Reserve
A narrow cut through the Belize Barrier Reef off the south tip of Ambergris Caye, Hol Chan (“little channel” in Maya) was declared Belize’s …
Gear
What to bringSite-specific add-ons
Some dive sites here call for extra gear. Check the individual site page for full context.
- SMB + reel — Wall drifts end in open water. · Half Moon Caye Wall
- Macro camera — Garden eel and spotted drum colonies reward a long lens. · Long Caye Ridge
What divers say
“The Blue Hole itself is more impressive from the air than underwater — but the wall dives on the way home are quietly some of the best Caribbean diving I've ever done.”