Two French tourists died while snorkelling on Australia’s Great Barrier Reef.
The elderly pair, a man and a woman, were found unconscious in shallow water at a popular tourist spot near Cairns in Far North Queensland, police said.
Local reports suggested the man and woman, who were in their 70s, had suffered from cardiac arrests.
However a medical expert says that doesn’t add up and has put forward a theory they have died due to deadly jellyfish.
Sydney cardiologist Dr Ross Walker thinks an Irukandji jellyfish may be the culprit.
"Irukandji are the size of your little fingernail, they’re very small, you can’t see them," he told reporters.
"It’s highly unlikely that two people are going to die within minutes of each other just because they’ve got underlying medical conditions."
Irukandji is one of the deadliest sea creatures and it takes about 20 minutes after a sting before the venom sends the body into cardiac arrest.
They were snorkeling at Michaelmas Cay, about 25 miles from Cairns when first the man was spotted in distress, then the woman.
A lookout pulled the man to the beach where he attempted to resuscitate him and a second lookout on a boat hauled the woman onboard.
The chief of the Association of Marine Park Tourism Operators told the BBC that the pair had indicated that they had pre-existing medical conditions before entering the water and the company had guides swimming around the snorkellers.
Passions of Paradise CEO Scotty Garden said in a statement: "It is very stressful for our staff but their priority has been with helping the group."
