An Israeli father-son team aiding in the effort to rescue a Thai soccer team trapped in a flooded cave are casting doubts over the viability of extracting the group through the water, saying it could end in a “catastrophe.”

Thai authorities are racing to pump out water from a flooded cave where 12 boys and their soccer coach have been trapped since June 23, before more rains are forecast to hit the northern region. Officials have also said they are considering trying to bring the boys out by having them dive and swim through the flooded cave.

The gargantuan extraction effort hit a setback Thursday night when a former navy seal, volunteering at the site, died after he ran out of oxygen during a dive in the labyrinthine cave.

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Rafael Aroush, who has lived in Thailand for decades, said the death underscored the difficulty that the boys, aged 11-16, and their 25-year-old coach, will face in trying to swim out of the cave.

“It’s very risky [diving out]. Think about it, a Navy Seal just passed away last night, so how about a 12-year-old kid,” said Aroush.

Aroush on Thursday drove with his son Shlomi from his home in Udan Thani province to the Tham Luang Nang Non cave to help with the rescue effort, joining other Israelis also providing support at the site.

“There’s water everywhere, it’s very, very, very tight, you’re going between narrow passages with a lot of water,” he told reporters standing outside the cave Friday.

“Many things could go wrong … it could be a catastrophe,” he said. “The conditions are really hard. Bad visibility. Dangerous for the most experienced divers to go through.”

A former navy SEAL working to rescue boys trapped in a Thai cave has died from lack of oxygen. "The conditions are really harsh. Bad visibility. Dangerous for the most experienced divers…A navy SEAL died last night, that says a lot about it" – Rafael Aroush – Volunteer diver. pic.twitter.com/u254h8qgnu — 7 News Perth (@7NewsPerth) July 6, 2018

Rafael, 53, said he had visited the cave 25 years ago and found it especially difficult to navigate, according to Reuters.

“It’s very narrow. The way divers have to work is not a normal way of diving. The visibility is also really bad. You’re diving blindly,” Aroush told the news agency.

Compounding the difficulties is the fact that the boys have no experience swimming and are atrophied after some two weeks in the cavern, where they became trapped after going exploring following a soccer practice.

On Thursday, Chiang Rai provincial Governor Narongsak Osatanakorn said he asked the SEALs in charge of extraction plans to estimate what level of risk would be involved to bring out the boys and their coach even though they weren’t 100 percent ready for a perilous hours-long dive.

Officials prefer to get the boys out as soon as possible because heavy rain expected by Saturday almost surely will raise water levels again in the cave, making passage in some areas even more difficult, if not impossible. They are hoping that an upgraded draining effort can lower the water in an area where it is still at or near the ceiling. The idea is to get some headroom so the boys would not be reliant on scuba apparatus for a long stretch and could keep their heads above water.

“We can no longer wait for all conditions (to be ready) because the circumstance is pressuring us,” Arpakorn said. “We originally thought the boys can stay safe inside the cave for quite some time but circumstances have changed. We have a limited amount of time.”

The governor has said the 13 may not be extracted at the same time, depending on their condition. They’ve practiced wearing diving masks and breathing, in preparation for the diving possibility.

Cave rescue experts have said it could be safest to simply supply the boys where they are, and wait for the flooding to subside. That could take months, however, given that Thailand’s rainy season typically lasts through October.

A sombre mood has clouded the elation from earlier in the week, when the boys were found disheveled and hungry but alive on a ledge kilometres inside the cave.

The navy seal who died in the cave, identified as Saman Kunont, had been part of a team trying to establish an oxygen line to the chamber where the children are awaiting rescue.

The complexity of the cave was underscored by the need for a special communications system, which an Israeli team from the firm Maxtech rushed out to set up earlier this week.

In the system, a string of small devices, similar to handheld radios, pass wireless communications between each other, enabling a link in places regular radios won’t work, such as where there are major obstacles blocking the line-of-sight between the two ends of the line.

It took 19 of the devices to complete the link to the boys in the cave. They have enough battery power for 10 hours’ use at a time.

“It is like a daisy-chain,” Uzi Hanuni, CEO of Maxtech told The Times of Israel on Thursday. “It is a very complex scenario inside the cave.”

Stuart Winer and AFP contributed to this report.