Deep beneath the crystal turquoise water, white sandy beaches and thatched overwater bungalows of the Maldives lies a deep and narrow system of caves, devoid of light and the colorful marine life that inhabits higher waters.

The seas were rough and the wind was picking up late Thursday morning when a team of five experienced Italian divers plunged toward these pitch-black caverns off the Vaavu Atoll, about an hour south by speedboat of the capital Malé.

The group included instructor Gianluca Benedetti; Monica Montefalcone, an associate professor of ecology at the University of Genoa; her daughter Giorgia Sommacal; marine biologist Federico Gualtieri; and researcher Muriel Oddenino.

The divers ventured deep into the cave network, which opens at a depth of about 47 meters (154 feet) and drops to about 70 meters (230 feet) at its lowest point.

They never returned.

The bodies of the five scuba divers were only found after a multi-day search effort, a fraught and perilous process which claimed a sixth victim, local military diver Sgt. Mohamed Mahudhee.

The group had permission to dive deeper than the 30 meters (98 feet) Maldivian recreational dive limits allow, local authorities said.

But it’s not clear whether they went deeper than planned, or whether they had the appropriate equipment for such a high-risk expedition.

A frantic search

The divers were staying on board a luxury 36-meter yacht called the Duke of York that offers customized cruises for up to 25 guests.

An ocean lover’s dream, the yacht allows divers to explore the Maldives’ coral islands up close, while enjoying seafood dinners and days spent lounging on sun beds on the top deck.

Around 1:30 p.m. Thursday, someone aboard the boat put out a distress signal, Mohamed Hussain Shareef, the chief spokesperson for the Maldives government told CNN.

The divers had been underwater for about two hours and had failed to resurface.

Another liveaboard vessel responded first, Shareef said. Within about half an hour, divers from that vessel located Benedetti’s body at the mouth of the cave.

The Maldives Coast Guard began an over and underwater search for the four remaining divers, but once Benedetti’s body was found, the authorities began working under the assumption that the four remaining divers were inside the cave.

Monica Montefalcone was an environmentalist who had conducted marine research in the Maldives for many years.

Her husband Carlo Sommacal, Giorgia’s father, said his wife was “one of the best divers on the face of the earth.”

“She must have completed 5,000 dives,” Sommacal told Italian newspaper la Repubblica.

Ahead of the dive, the Maldives’ Marine Research Center had approved a research proposal from Montefalcone, Gualtieri and Oddenino to study soft corals near the Vaavu Atoll, Shareef said. Sommacal and Benedetti were not listed on the application.

The Italian researchers had also obtained permission to conduct technical dives, meaning they could explore deeper than 30 meters, Shareef said.

But the Maldives authorities did not know the divers would be cave diving, Shareef said, or they would have lent the support of the Coast Guard or other professionals to assist with the complex dive.

“We are very sure that we would have been able to give them much clearer guidelines and advice had they told us that this was such a demanding assignment at such depths inside a cave.”

The University of Genoa said Montefalcone and Oddenino were in the Maldives to study the effects of climate change on biodiversity, but that the dive itself “was not part of the mission’s planned activities” and was “carried out on a personal basis,” according to Reuters news agency.

Further increasing the riskiness of the dive was poor weather. The Maldives Meteorological Service issued a white alert mid-morning Thursday, warning of strong winds and rough seas. It’s not clear whether the divers knew about the alert.

By mid-afternoon, the warning level was raised to yellow, with strong winds of up to 30 miles per hour with gusts of 50 miles per hour, and very rough seas.

A hard-to-access underwater ecosystem

Few divers have ventured into this rare underwater ecosystem; Vladimir Tochilov, a Russian technical diving expert, is one of them.

“This cave is accessible only for technical cave divers who have the appropriate preparation, the appropriate experience and who are planning on correctly diving into this cave,” Tochilov told CNN.

The cave where the Italians were found is about 200 meters long and consists of several halls, according to Tochilov, who dove there in 2014.

A video posted to YouTube by Tochilov’s diving company, Neva Divers, reveals a dark, barren and otherworldly ecosystem.

At points the divers, illuminating their route with flashlights, must swim through narrow corridors. It appears foreboding and claustrophobic.

Tochilov says cave diving requires not only intensive technical training but psychological preparation to deal with the feeling of fear and disorientation.

As you go deeper into the Maldives cave, you reach a point where the light of the exit is no longer visible, and you need to navigate in complete darkness, Tochilov said.

“Any person, if you try to spin them in the dark and ask to find an exit in a dark room, there will also be difficulties,” Tochilov said.

Unlike other popular diving destinations, the Maldives is not known for cave diving. The cave the divers were exploring may be the only one like it in the area, Tochilov said.

“This is probably why it attracted the attention of divers, including scientists, biologists, and researchers,” he said. “The cave has its own flora and fauna that you will not see outside the cave.”

A dangerous recovery mission

Following the discovery of the dive instructor’s body on Thursday, it would take until Monday for the remaining four divers to be located, within the third chamber of the cave, according to Maldives authorities.

The multinational search operation involved local experts, three Finnish divers from the global scuba safety group Divers Alert Network (DAN) and specialist equipment provided by the United Kingdom and Australia, Shareef said.

Unpredictable strong currents, narrow passageways in the caves and pitch-black darkness made the operation extremely challenging, Shareef said.

“You have to be an expert for this level of diving,” he added.

The search effort was suspended for a day after Mahudhee, the senior military diver, died on Saturday.

Authorities believe he died from decompression sickness, which occurs when divers ascend too quickly and there is a rapid decrease in pressure around them.

Mahudhee was laid to rest with full military honors at a ceremony in Malé, where thousands paid their respects including President Mohamed Muizzu, tourism and military officials and foreign ambassadors.

Authorities probing diving vessel

It’s not yet clear what happened to the Italian divers.

Deep-sea cave diving brings a host of risks, said John Volanthen, a diving officer for the British Cave Rescue Council, who played a key role in the rescue of a Thai youth soccer team that became trapped in a labyrinthine underwater cave network in 2018.

A dozen boys and their coach were safely removed from the flooded Chiang Rai cave system after a daring and extraordinary effort to bring them out one by one.

One of the dangers of deep-sea diving is gas narcosis, an anesthetic effect experienced by scuba divers which is caused by breathing compressed gas at depth. Divers often use specialized breathing mixtures, such as nitrogen and oxygen, to prevent this condition.

Volanthen says the Italian divers may have become confused while deep inside the cave.

“As you start to go deeper, that narcosis effect could potentially create panic, but it could also make them less likely to be able to find their way out,” Volanthen said.

Shareef said authorities are focusing their inquiry on the yacht and have suspended its license while they investigate further.

“We know for a fact that the vessel did not have all its papers in order,” Shareef said, adding that the vessel lacked a “dive school license.”

“If you’re going to run a dive school operation, where you are advertising and assisting clients on diving missions, whether it’s recreational or technical, you need to have a dive school license,” he said.

CNN has reached out to the operator of the Duke of York, Abdul Muhsin Moosa, for comment. He told Reuters the vessel had permission for dives of up to 30 meters, and divers were briefed on arrival about the limit.

Orietta Stella, lawyer for Albatros Top Boat, the Italian tour company which sold trips on the yacht, said the boat’s operator “did not know” the group planned to descend further than the recreational dive limit and “would never have allowed it,” according to the Associated Press.

She also clarified that Albatros only marketed the cruise and neither owned the vessel nor employed the crew, which was hired locally. CNN has contacted Albatros Top Boat for further comment.

As authorities try to determine what led to the loss of five lives, Sommaca is left to grieve a wife and daughter.

Montefalcone was a “conscientious person” who would never have put others’ lives at risk, he told la Repubblica.

“Something must have happened down there.” (CNN)

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