A British tourist has died on a trip to the Great Barrier Reef after swimming in an area believed to be infested by killer jellyfish. A rescue helicopter was sent but emergency response crewmembers could not revive the man.

The 63-year old man is said to have been just feet away from the reef pontoon when he had a heart attack while clinging to a safety ring, reports Fox News. The incident occurred on Moore Reef, 25 miles off the coastline of Cairns, in Queensland, Australia. This is the fifth death in the last three months at the Great Barrier Reef.

On the same day, a 43-year-old woman was brought to hospital by helicopter to Cairns Hospital in a critical condition after being rescued from the water off Green Island. The woman was already unconscious when found. Just last January 30, three children from China and Japan suffered suspected Irukandji stings near Fitzroy Island which is less than 20 miles from Moore Reef.

Last November, two French tourists died only minutes apart while they were snorkeling. Their deaths were followed by that of 60-year-old British scuba diver David Lowe from Sheffield, who was found on the ocean floor during a holiday with his wife.

There is a strong suspicion that the world's most venomous creatures, the Irukandji jellyfish are lurking off Ozzy coast after the series of incidents. This most recent incident could be also due to the sting of the Irukandji jellyfish in the area. At the time, cardiologist Dr. Ross Walker said, "I think it's highly likely they were stung by Irukandji. Irukandji are the size of your little fingernail, they're very small, you can't see them. Dr. Walker also said that it is very improbable that two people would die within minutes of each other even if they have underlying medical conditions.

Last month, several beaches in the area, including Three Cairns beach, were closed to the public following sightings of the jellyfish. Professor Jamie Seymour said that because the water temperature has increased, it allows the Irukandji jellyfish to go further and further south.