The Great Blue Hole: How Deep It Is and What’s Down There
The Great Blue Hole is 407 feet deep, and below 300 feet it is dead. An underwater photographer on what you see, what you don't, and whether it is worth the boat ride.
Diving the Great Blue Hole in Belize
By William Drumm, underwater photographer and ocean ambassador
From the boat it does not look real. Lighthouse Reef Atoll is a shallow turquoise plate, bright enough that you can see the sand grain through forty feet of water, and then in the middle of it there is a perfect dark circle, as if someone had punched a hole through the floor of the Caribbean and left it open.
You stride off the boat into water so clear it barely registers as water. You swim out across the shallow rim, maybe thirty feet under you, coral heads and grunts and a startled ray. And then the bottom quits. It does not slope away. It ends, at a hard edge, and beyond that edge is a dark shade of blue that every underwater photographer dreams about.
I have dived Belize three times over sixteen years: first in 2009, staying on Caye Caulker, then in 2018 out of San Pedro and Placencia, and most recently in 2025 on a photo shoot with Turneffe Island Resort. I have made the drop over the rim of the Great Blue Hole twice, in 2009 and again in 2025. What follows is everything I would tell a friend before they went: how deep it really is, what is down there, and whether it is worth the boat ride.
How Deep Is the Great Blue Hole?
The Great Blue Hole is 407 feet deep, or 124 meters. It is 1,043 feet across, roughly 318 meters, and almost perfectly round.
For context: recreational scuba tops out at 130 feet. So on a normal Blue Hole dive you go down about a third of the way, hang there for a few minutes, and come back up. The other 277 feet are not part of the trip. For a long time nobody really knew what was in them.
Then, in late 2018, somebody went and looked.
What Is at the Bottom of the Blue Hole
In November and December of 2018 an expedition run by Aquatica Submarines put two crewed submersibles into the Blue Hole and made more than twenty dives to the floor. Richard Branson rode down in one of them. So did Fabien Cousteau, whose grandfather Jacques had brought the *Calypso* here in 1971, blasted a channel through the reef to get in, and told the world it was one of the finest dive sites on Earth. The expedition produced the first complete 3D sonar map of the hole.
Here is what they found.
At about 300 feet, the water changes. There is a layer of hydrogen sulfide, and below it the Blue Hole is anoxic. No oxygen. No light. Nothing living. The subs described dropping through it as passing into a different fluid, and the cameras went from blue to nothing. The bottom 100 feet of the Great Blue Hole is a dead zone that has probably been dead for thousands of years.
They found conches at the bottom. Snails that had wandered over the rim in the shallows, fallen, and suffocated. They are lying down there in the sediment with a trail behind each one, showing the last few feet they crawled before the water killed them. The expedition called it the conch graveyard.
They found two people. Divers who had gone missing in the hole, never recovered. The team reported the locations to the Belizean authorities and did not disturb them.
And they found trash. Less than a hundred feet from the floor of one of the most remote and celebrated dive sites in the world, in water no human being had ever seen, there were plastic bottles and a lost GoPro. That is the detail I have not been able to shake. There is nowhere left that is only water.
How the Blue Hole Formed
The Blue Hole is not a marine feature. It is a cave, and it was made in the air.
During the last glacial period, when a great deal of the planet’s water was locked up in ice, sea level here was hundreds of feet lower than it is now. What is today Lighthouse Reef Atoll was dry limestone. Rainwater did what rainwater does to limestone: it dissolved it from the inside, opening rooms and passages, and inside those rooms, over tens of thousands of years, stalactites grew down from the ceiling.
Then the ice melted. The sea came back. And at some point the roof of the largest chamber gave way and dropped into itself, leaving a shaft open to the sky.
The stalactites are still there. At around 130 feet, on the ledge where recreational divers turn, they hang under an overhang in rows, some of them longer than a person. And they hang at an angle. Not vertical. Tilted, all in the same direction, which means the entire block of rock rotated after they had already formed and hardened.
You are swimming through the wreckage of a cave that was never wet when it was being built. That is what you have come to see. The formations are massive, far bigger than photographs prepare you for, and it is the most geologically strange thing I have ever put a camera on.
What Diving the Blue Hole Is Like
It is truly one of the coolest dives in the world. But it is unique, and might not be what you are expecting.
The Blue Hole is a deep bounce dive. You descend along the wall in the blue, you level off at around 130 feet, you swim under the overhang and past the stalactites, you take your photographs, and you come back up. Bottom time at that depth is short. You will be watching a computer the whole time. Narcosis is real down there and it is sneaky; you will feel calm and capable and slightly delighted, which is exactly the problem.
The visibility inside the hole is worse than outside it. People expect the water to be gin clear because the water on the reef is gin clear. It is not. It is dim and slightly green and the walls swallow your strobes. It photographs like a cathedral, not like a coral reef. The divemaster on my 2025 trip told me the visibility inside had become less dependable since around 2018. Some days it is good, some days less so, where it used to be more consistent.
The wildlife is thin. You may see Caribbean reef sharks, and you probably will, cruising the wall in that unhurried way they have. Occasionally a bull shark or a hammerhead comes up out of the dark. Mostly you see rock.
None of that makes it a bad dive. It makes it a different kind of dive. You are not there for animals. You are there for scale and for age and for the specific feeling of hanging in open water with 277 feet of dead ocean underneath you. Across both of my trips it was, without hesitation, my favorite dive. I have not felt anything else quite like it.
One caution, because it matters here more than almost anywhere: it is very easy to go too deep on this dive. There is no bottom under you to check yourself against, just blue that keeps going. I would not do the Blue Hole without at least an Advanced Open Water certification and, honestly, fifty or more logged dives behind you. It is not formally required, but you will have more fun and be a great deal safer with some real depth experience in your body first.
Is the Blue Hole Worth It?
Yes. Absolutely.
A Blue Hole trip is a full day, usually three tanks. The Blue Hole is the first, because it is the deepest. Then the boat moves to Half Moon Caye Wall and Long Caye Wall, and those are genuinely world-class dives. On my 2025 trip Half Moon Caye was the wild one: insanely clear water, vertical walls falling into indigo, huge sponges and sea fans, eagle rays, turtles everywhere, and groupers that swim right up to you and hold there like they want their portrait taken. All the life that the Blue Hole does not have.
Half Moon Caye is also a Natural Monument and the site of a red-footed booby colony, and the surface interval is spent on a beach that looks like a screensaver, with frigatebirds harassing the boobies overhead.
So do the Blue Hole. Tick it. Take the photograph. But understand that you are buying a whole day, and the day is worth it even if the hole itself is only the opening act.
Hol Chan Marine Reserve
Hol Chan means “little channel” in Mayan, and that is exactly what it is: a natural cut through the barrier reef a few miles south of San Pedro, where water pours in and out with the tide and everything that eats comes to eat.
It was established in 1987, and it was the first marine protected area in Belize, and one of the first anywhere in Central America. It worked. Decades of no fishing have produced a reef with the one thing most Caribbean reefs no longer have: big fish, in numbers. Groupers that do not flinch. Barracuda hanging in the current like suspended knives. Green morays out and swimming in the open, which is not something you see often.
The channel is shallow, around thirty feet, which means long dives and beautiful light. In 2018 I was based in San Pedro at Ramon’s Village, ten minutes away, and the night dive we did at Hol Chan is still one of the best I have done anywhere. After dark the whole system changes shift: an octopus out and hunting across the sand, eagle rays and stingrays gliding through the beam, spider crabs, sleeping fish tucked into the coral, and the morays moving fast and openly in a way that is genuinely unnerving the first time you see it in a light beam. It is shallow enough that the dive runs long, and beautiful enough that you do not want it to end.
Shark Ray Alley
Shark Ray Alley is the second zone of Hol Chan, added to the reserve in 1999, and it exists for a reason that is entirely human.
For years, fishermen coming back through the cut would stop on that patch of shallow sand to clean their catch and dump the scraps. Nurse sharks are not stupid. Neither are southern stingrays. Within a few seasons, the sound of a boat engine slowing at that spot meant food, and dozens of animals would materialize out of the turtlegrass.
The fishing stopped. The animals stayed. Now you slide into eight feet of water and there are nurse sharks stacked underneath you like firewood, six and eight feet long, and stingrays coming in low across the sand with their wingtips turning up.
It is not a wild encounter and I would not pretend it is. It is a habituated aggregation created by decades of provisioning. But it is a completely safe way for a nervous person to be in the water with a shark and discover that nothing happens, and I have watched that realization change people’s faces. That has value.
Bring the water home
The Belize Barrier Reef
The Belize Barrier Reef is the second largest reef system in the world, after Australia's, and it is the largest in the northern hemisphere. It runs roughly 190 miles along the coast and forms the biggest section of the Mesoamerican Barrier Reef System, which continues north into Mexico and south to Honduras.
It has been a UNESCO World Heritage Site since 1996. In 2009 UNESCO put it on the List of World Heritage in Danger, because of mangrove clearing, coastal development and, above all, the prospect of offshore oil drilling.
In 2018 it came off that list. Belize had done something almost no country does: it passed a moratorium banning oil exploration in its entire maritime zone. The whole thing. It is one of the few genuinely good pieces of news in ocean conservation this century, and it is worth knowing when you are floating over the reef that it is there partly because a very small country decided it would rather have coral than crude.
Belize also has three of the four true coral atolls in the western hemisphere: Lighthouse Reef (which holds the Blue Hole and Half Moon Caye), Turneffe Atoll (the largest, and the least crowded), and Glover's Reef.
Snorkeling in Belize
You do not always need a tank here. Some of the best water in Belize is ten feet deep.
Hol Chan and Shark Ray Alley are the classic half-day snorkel out of San Pedro, and they are the right call: the channel is shallow enough to see everything from the surface, and Shark Ray Alley is a snorkel site more than a dive site anyway.
Ambergris Caye has good shallow reef right off the beach in places, plus Mexico Rocks, a shallow patch reef north of San Pedro that is ideal for kids and first-timers.
Placencia, down south, is the jumping-off point for Gladden Spit, where whale sharks aggregate around the full moons of March through June to feed on snapper spawn. It is not a sure thing and it never has been, but when it happens it is one of the great animal encounters in the Caribbean. I have not been lucky enough to photograph whale sharks in Belize myself; the whale shark image on this page is from Mexico. If you want the biology of these animals, I wrote a whole piece on whale sharks.
Snorkeling and Diving Caye Caulker
Caye Caulker deserves its own section, because it is where most people should stay, and it is where my own history with Belize began.
My first trip, back in 2009, I stayed on Caye Caulker and dived the Blue Hole from there. It is a longer, more exposed crossing than the run from San Pedro, and the ride home that day was one of the roughest boat rides I have taken, weather stacking up the whole way back. But Caulker itself was worth it. It is the smaller, scruffier, cheaper island north of Ambergris, and its unofficial motto is painted on a sign as you get off the boat: Go Slow. There are no cars. There is sand instead of roads. There is a place where the island was cut in half by a hurricane, called the Split, and everybody swims there and drinks there at sunset. There was a man selling lobster door to door when I was there. That is the register of the place.
And the snorkeling off it is superb, and it is cheap.
The Caye Caulker Marine Reserve sits right off the island, and the classic half-day snorkel trip out of Caulker hits Coral Gardens, the Swash and often Shark Ray Alley and Hol Chan as well, because Caulker boats run south to the same reserve that the San Pedro boats do. You can do the whole famous circuit from Caye Caulker and it will cost you less.
What makes Caulker snorkeling different from San Pedro's: the boats are smaller, the groups are smaller, and there is a much stronger culture of sailing rather than motoring. A day on a small sailboat with six people, three snorkel stops and rum punch on the way home is one of the great cheap pleasures in the Caribbean, and it is what Caye Caulker is for.
Diving Caye Caulker. There are good dive shops on the island, and they run the local reef, Hol Chan, and the Blue Hole day trip, same as San Pedro. If you are diving the Blue Hole from Caulker, the crossing is longer and it is an exposed run, so it gets canceled in weather. Factor that in.
Manatees. Caye Caulker sits near seagrass flats and manatee-watching trips run from here. Look, do not chase, and do not get in the water on top of them.
When to Go
Belize dives well all year. Water temperature sits between about 79°F and 84°F, so a 3mm suit is plenty and in summer plenty of people wear a rash guard.
April to June is the best window. Visibility is at its peak, the sea is flat, the Blue Hole trip runs (it gets canceled in rough weather, and it is a long crossing), and the whale sharks are at Gladden Spit.
Hurricane season runs June to November, with the real risk concentrated in September and October. Some operators close.
December to March is high season, dry and pleasant topside, but with more wind. Blue Hole trips get blown out more often than people expect, so if the hole is the whole reason you came, do not book your one shot at it on your last day.
Where to Base Yourself in Belize
I have dived Belize from three very different bases, and which one is right for you depends entirely on what you want out of the trip.
Turneffe Island Resort (Turneffe Atoll). My 2025 trip was a photo shoot based at Turneffe Island Resort, a secluded 14-acre private island at the southern end of Turneffe Atoll, about 35 miles and a 90-minute boat ride from Belize City. It is the kind of place that takes up its whole island: comfortable rooms, excellent food, and more than thirty dive sites within reach of the dock, including the famous drift dive at the Elbow on the atoll's point. Turneffe is the largest of Belize's three atolls and the least crowded, and the resort runs the full-day Blue Hole and Lighthouse Reef trip once a week. Because guests arrive and leave only twice a week, it is quiet in the best way. If you want to dive hard, eat well, and see almost no one else, this is the base I would go back to.
San Pedro, Ambergris Caye (Ramon's Village). In 2018 I was based in San Pedro at Ramon's Village, and it is the easiest diving I have ever done. The dive boats are tied up at the resort, the sites are five to fifteen minutes from the dock, and you are minutes from Hol Chan. If you want a town at the end of the day, with restaurants, golf carts, and a proper base with the shortest run to the reserve, San Pedro is the pick, and you can still reach the Blue Hole on a day trip.
Caye Caulker. My first trip, in 2009. This is the budget, no-cars, go-slow option: same reef, same marine reserve, same Blue Hole day boat, for less money and with a better sunset. The Blue Hole crossing from Caulker is longer and more exposed, so build in schedule slack if the hole is your priority.
Whichever base you choose, if you are going to do the Blue Hole, be honest with yourself about your depth experience. This is not the dive on which to discover how you handle 130 feet.
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Photographing Belize
The Blue Hole is a wide-angle-only dive, no exceptions. The subject is the wall, the stalactites and the human being for scale. You will not get color out of it, so stop fighting for color: shoot it for shape, silhouette the diver against the rim above you, and let it be a cathedral. Strobes are close to useless on the big stuff. Use them on the stalactite in the foreground and let the rest fall into blue.
Half Moon Caye is where you get the postcard. Wall, sunball, eagle ray. Get shallow, shoot up, expose for the water and let the strobes do the reef.
Hol Chan at night is a macro playground, and the octopus are the prize. Red light if you have one; white light on a hunting octopus ends the hunt.
Shark Ray Alley is a lens choice, not a photograph. It is chaos, it is eight feet deep, and there are seventeen other snorkelers in every frame. Go wide, get low on the sand, shoot upward so your background is the surface and not somebody's fins, and be patient. The one good frame comes when a nurse shark drops over you and the light comes through it.
Frequently Asked Questions
How deep is the Great Blue Hole in Belize?
The Great Blue Hole is 407 feet deep, which is 124 meters. It is 1,043 feet across, about 318 meters, and roughly circular.
What is at the bottom of the Blue Hole?
Sediment, sunken conch shells, and nothing alive. A 2018 Aquatica Submarines expedition, which included Richard Branson and Fabien Cousteau, mapped the floor and found a layer of hydrogen sulfide at around 300 feet. Below that the water is anoxic, so there is no oxygen and no life. They also found the remains of two divers who had gone missing, and, near the bottom, plastic bottles and a lost GoPro.
How was the Great Blue Hole formed?
It was a limestone cave, formed on dry land during the last glacial period when sea level was hundreds of feet lower. Stalactites grew inside it in open air. When the ice melted and the sea rose, the roof of the main chamber collapsed, leaving a vertical shaft. The stalactites are still there at around 130 feet, tilted at an angle, which shows the whole block of rock shifted after they formed.
How deep do you dive in the Blue Hole?
Recreational dives go to about 130 feet, which is roughly a third of the way down. Bottom time at that depth is short, usually around eight minutes. Technical divers go deeper, but there is very little reason to: below the stalactite ledge there is nothing to see until the dead zone.
Is the Blue Hole a good dive?
It is a remarkable dive, but not a good wildlife dive. Visibility inside is poorer than on the surrounding reef, the light is dim, and you will see a handful of Caribbean reef sharks at most. Go for the scale and the geology. The two dives you do afterwards, Half Moon Caye Wall and Long Caye Wall, are better dives by any normal measure.
Are there sharks in the Blue Hole?
Yes. Caribbean reef sharks patrol the walls and are seen on most dives. Bull sharks and hammerheads turn up occasionally. None of them present a problem. There are far more sharks at Shark Ray Alley, and those are nurse sharks, which are harmless.
Can you snorkel the Great Blue Hole?
You can float over it, and boats will take you, but there is nothing to see from the surface. The walls and stalactites begin far below snorkeling depth. If you are not a diver, spend the day snorkeling Half Moon Caye and Hol Chan instead, which are genuinely spectacular from the surface.
Where is the Great Blue Hole?
It sits in the middle of Lighthouse Reef Atoll, about 43 miles off the coast of Belize and roughly two hours by fast boat from San Pedro on Ambergris Caye. It is a long, exposed crossing and trips are canceled in rough weather.
What is the best time to dive in Belize?
April to June. Visibility is at its best, the sea is calmest, the Blue Hole crossing runs, and whale sharks aggregate at Gladden Spit around the full moon from March to June. Hurricane season is June to November, with the highest risk in September and October.
How big is the Belize Barrier Reef?
It runs about 190 miles along the Belizean coast and is the second largest reef system in the world after the Great Barrier Reef. It forms the largest section of the Mesoamerican Barrier Reef System. It has been a UNESCO World Heritage Site since 1996, and in 2018 it was removed from the List of World Heritage in Danger after Belize banned offshore oil drilling in its entire maritime zone.
Why are there so many nurse sharks at Shark Ray Alley?
Fishermen used to stop at that spot to clean their catch and dump the scraps, and nurse sharks and southern stingrays learned that a boat engine slowing there meant food. The fishing stopped when the area was protected in 1999, but the animals stayed. It is a habituated aggregation, not a wild one, but it is completely safe and it is a good place to be in the water with a shark for the first time.
Is Caye Caulker good for snorkeling?
Very. The Caye Caulker Marine Reserve is right off the island, and Caulker boats also run south to Hol Chan and Shark Ray Alley, so you can do the entire famous circuit from there. Trips are smaller, cheaper and often under sail rather than motor. If your priority is getting in the water a lot without spending much, stay on Caye Caulker rather than San Pedro.
Should I stay on Caye Caulker or Ambergris Caye?
Ambergris Caye and its town, San Pedro, is the bigger, more developed base: resorts, restaurants, golf carts, and the shortest run to Hol Chan. Caye Caulker is smaller, cheaper and slower, with no cars and sand streets. Both reach the same reef, the same marine reserve and the same Blue Hole day trip. Caulker's Blue Hole crossing is longer. For a quiet dive-focused base away from both, Turneffe Atoll is the third option.
Where is Half Moon Caye?
Half Moon Caye is in Belize, on Lighthouse Reef Atoll, and it is a Natural Monument with a red-footed booby colony. It is not the same place as Half Moon Cay in the Bahamas, which is a private cruise island and which dominates search results. In Belize, Half Moon Caye Wall is one of the finest dives in the country and it is usually the second dive on a Blue Hole day trip.
Do you need to be an advanced diver for the Blue Hole?
Most operators require an Advanced Open Water certification, and some ask for a minimum number of logged dives, because the profile takes you to 130 feet. That requirement exists for a reason. Nitrogen narcosis at that depth is real and it feels pleasant, which is precisely what makes it dangerous. If you have never been below 100 feet, do a few deep dives elsewhere in Belize first. I would want an advanced certification and around fifty dives behind me before dropping into the hole.
Sources
Depth, dimensions and the 2018 expedition findings verified against:
- Great Blue Hole — Wikipedia
- What Richard Branson, Fabien Cousteau, And Aquatica Submarines Found In Belize's Great Blue Hole — Forbes
- Belize's Great Blue Hole: Expedition learns what's below — CNN
- Aquatica Submarines Completes Historic Expedition to the Blue Hole of Belize — PR Newswire
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