Cave diving is fraught with danger, but the reward is sights like nothing else on Earth

Scuba divers pictured exploring an underwater cave in Croatia in 2023. (Marko Djurica/Reuters via CNN Newsource)

The light fades as divers disappear farther into a cave system, until the greenish hue from their flashlight is all that’s visible, bouncing off walls, picking out creatures humans might never have seen before, and illuminating a world otherwise confined to total darkness.

These caverns can extend for hundreds of miles, dangerous, otherworldly mazes unlike anywhere else on Earth.

Any cave diver is well aware of the dangers involved in exploring these alien zones. In a 2024 documentary, “Diving Into the Darkness,” veteran Canadian cave diver Jill Heinerth recalls swimming “through the graves of my friends all the time. That list is well over a hundred people.”

The dangers of this highly specialized discipline were underscored once again this month when five Italian divers died while exploring the Vaavu Atoll caves in the Maldives on May 14, and Maldivian military diver Sgt. Mohamed Mahudhee also died attempting to recover their bodies.

Diving instructor Gianluca Benedetti’s body was found at the mouth of the cave, and the other four divers — Monica Montefalcone, an associate professor of ecology at the University of Genoa; her daughter, Giorgia Sommacal; Federico Gualtieri, a marine biologist; and Muriel Oddenino, a researcher — were all found in the deepest part of the cave system.

But even though they are acutely aware of the dangers, something constantly draws back cave divers who dedicate, and sometimes sacrifice, their lives to exploring these strange underwater worlds.

Navigating only with flashlights and a guideline — the thin thread that allows divers to find their way back to the cave entrance — they glimpse another side to life on Earth.

Cave divers often describe their chosen habitat as space-like, a whole other world filled with stalagmites, stalactites and alien-like creatures. Diving in these underwater cave systems is like “swimming through the veins of Mother Earth,” said Heinerth, who has completed more than 8,000 dives.

“Astronauts have that overview effect where they talk about looking back on the great blue planet, and they can never look at Earth the same way again,” she told CNN on Tuesday. “I guess I’m having a similar effect from being inside the planet … I’m literally within the sustenance of the planet that’s supplying the water for humanity, wildlife and even all of the industries we require for our modern life.”

‘All the things that could go wrong’

So many things can go wrong during a cave dive. Equipment can fail; guidelines can break; visibility can become nigh on impossible. And, if things go wrong, you cannot just ascend to the surface as in other types of scuba diving. You are reliant on your own wits, and your dive buddy.

While exploring these systems, cave divers will routinely squeeze through incredibly tight spaces. Sometimes, “my shoulders are scraping the ceiling and my belly is on the floor, and I can see less than a metre in high flow as the sand and silt is blasting me in the face,” Heinerth said.

So, before any dive, before she does anything else, Heinerth will “rehearse all of those things that could go wrong, all of the things that could kill me in this environment.”

“Like, what if this hose suddenly breaks and I’m losing gas, can I reach this valve in the gear that I’m wearing today?” she says.

“But it’s also a deep self-assessment. Am I ready to do such a dive? And the last two questions I ask myself are, ‘Am I ready for self-rescue today with the gear that I have in the environment that I’m in?’ and ‘Am I willing and able to conduct a buddy rescue in the same situation?’”

At the same time, she added, cave divers are normally incredibly well-trained and prepared for any scenario.

“The last step I take is I leave the emotions on the surface … You really have to stay in a pragmatic brain ready to deal with any situation that can occur,” she said.

It isn’t yet known why the five Italian divers never surfaced from their dive in the Maldives, though an investigation is underway to establish what happened — and how they all reached such depths.

The group had permission to dive deeper than the 30 metres (98 feet) to which recreational dives in the Maldives are normally restricted, local authorities said.

But it still isn’t clear whether they went deeper than planned, or if they had the appropriate equipment for such a technical, risky dive.

Caves like these are a rarity in the Maldives, Vladimir Tochilov, a technical diving instructor who has explored this system before, told CNN. It’s only 200 metres (656 feet) long and consists of several halls, but its depth “requires serious, serious training.”

Underwater treasure troves

Underwater cave systems are treasure troves of information, providing an important source of data for biologists, physicists, paleontologists and historians.

“These caves are like museums of natural history, providing information on the Earth’s past climate, on animals that live their entire life in the darkness, and also on ancient civilizations that have viewed these places as portals to another world,” Heinerth said.

Some cave systems host endemic species, meaning that they are found in no other place on the planet. By documenting such species, cave divers have helped inform our understanding of the planet’s evolutionary history.

Heinerth has visited some caves that no other human has ever explored, and probably never will again. As an underwater photographer, “bringing back images from these places that makes people’s jaws drop is very fulfilling because it gives me a chance to share the adventure,” she said.

Always, however, she is wary of the dangers. “My choices about risks will not just affect me, but it’ll be my family, my community,” she said. “So we need to learn from accidents, communicate honestly about what went wrong and how we can prevent them in the future.”