Tom and Eileen Lonergan were an adventurous couple who had travelled the world together and had always loved to scuba dive. But when they headed to the Great Barrier Reef in 1998, they would never return

For many, experiencing Australia's Great Barrier Reef is the ultimate holiday of a lifetime. Located off the coast of Queensland, this natural treasure, which is one of the world's seven wonders, attracts visitors from across the globe.

During January 1998, Tom and Eileen Lonergan, an American couple, boarded a scuba diving vessel known as the Outer Edge, to marvel at the reef's splendour up close. Unfortunately, they would never return to dry land.

Just like the other passengers on board, the Lonergans spent over 30 minutes exploring the ocean's depths, taking in the breathtaking coral and diverse marine life. However, when they resurfaced, their boat was nowhere in sight.

It was later revealed that the vessel's crew hadn't noticed the couple's absence and had sailed off without them. It took two days for the realisation to sink in, at which point rescue teams rushed to scour the shark-prone diving spot, but there was no sign of 33-year-old Tom or 28-year-old Eileen.

As the search operation progressed, detectives discovered the couple's personal journals in their hostel room in Cairns, a city in the north of Australia's east coast. Their contents were unsettling, to say the least, reports the Irish Star .

In his diary Tom wrote: "I feel as though my life is complete and I'm ready to die," a disturbing entry dated six months prior to the couple's disappearance. He added: "As far as I can tell, from here my life can only get worse. It has peaked and it's all downhill from here until my funeral."

Eileen voiced her concerns over her husband's seemingly indifferent stance on death in one of her final diary entries, penned just 16 days before the pair went missing.

She wrote: "Tom hopes to die a quick and fairly painless death and he hopes it happens soon. Tom's not suicidal, but he's got a death wish that could lead him to what he desires, and I could get caught in that."

The couple had tied the knot in their hometown of Baton Rouge, Louisiana, nine years before embarking on their fateful journey, having first crossed paths at Louisiana State University. Their shared zest for adventure led them to join the US Peace Corps in 1995, where they were tasked with teaching roles in Tuvalu and Fiji.

In January 1998, Tom and Elaine set off for Australia - the ultimate destination on their grand adventure before intending to head back home to the States. On Sunday, January 25, they hopped on a coach for an hour’s ride from Cairns to Port Douglas.

Upon arrival, they embarked on the Outer Edge for the expedition to St Crispin Reef, some 38 miles offshore.

They undertook two 40-minute diving sessions and were gearing up for a third dive at a spot known as Fish City. The locale was notorious for its abundant shark population around the reef, as confirmed by local fisherman Mick Bird, who was out at sea, not too far away that same day.

Fishing in the vicinity, Mick Bird said: '"Every time we threw a line, we'd pull in a shark - they should rename that place Shark City," the seafarer quipped.

When British scuba diver Bryan Brogdan appreciated a mammoth clam nestled in the coral next to the Lonergans, he was unaware it would be the couple's final sighting. After marvelling at the underwater spectacle together, Bryan swam back to the vessel, leaving the Lonergans submerged below for longer than the dive boat personnel had advised.

At 3pm, all divers were expected to convene on deck, prompting Geoffrey 'Jack' Nairn, former skipper of the Outer Edge, to ask his crewman George Pyrohiw for a headcount. This routine safety check wasn't executed accurately, resulting in a grave oversight.

The sequence that unfolded after the Lonergans didn't resurface constituted a succession of blunders, culminating in an astonishing timespan of over two days before anyone realised they were absent. As George Pyrohiw tallied the divers, two reentered the water to snap last-second photographs, causing a miscount.

Pyrohiw recounted to officials that he informed the captain there were merely 24 passengers aboard rather than the initial 26, to which the captain said: "And two in the water makes 26". Though Geoffrey Nairn contests this account, the tragic result remained unchanged.

Even after the Outer Edge arrived back at Port Douglas that evening and everyone had disembarked, two unclaimed dive bags left onboard did not raise suspicions. These belongings were just relocated elsewhere on the boat with the assumption being the owners would eventually ring up upon realising their mistake.

In addition to this oversight, an inventory check revealed that the vessel was short of two air tanks and two weight belts, yet no one raised any concerns. Norm Stigant, the driver responsible for transporting passengers back to their hotels, informed his superior that the Lonergans had not shown up for the ride - but he was told not to worry and eventually left without them.

As darkness fell, the American couple found themselves alone on the reef, with no one seemingly aware of the peril they were in.

The next day, the boat returned to St Crispin Reef with a fresh set of passengers, its crew still oblivious to the tragedy that had unfolded. Divers plunged into the water to admire the marine life, and soon two weight-belts were recovered from the ocean floor.

Astonishingly, this was another instance that should have triggered alarm amongst the crew - yet, they did nothing.

Another day passed, and the boat carried a new group of passengers before returning to Port Douglas for the second time since the Lonergans had failed to reboard. It was only at this point that the captain noticed the unclaimed dive bags still on the boat and decided to open them, where he discovered identification documents.

Amongst the items left in the bags were a shirt Tom Lonergan had worn on the day, and a wallet.

Finally, Geoffrey alerted the authorities. The police quickly found out that the couple's credit cards had not been used and a massive search operation was initiated.

However, it proved futile.

Ten days on, Tom's buoyancy jacket, bearing his name on the pocket, was discovered 50 miles north of St Crispin Reef. Additional items, including a shredded wetsuit, were also found.

Half a year later, in July, what was thought to be the couple's dive board turned up roughly 90 miles north of St Crispin Reef, retrieved by a fisherman. These boards are typically utilised for diver communication under the sea.

The board hauled in by the fisherman bore a desperate message that stated: "Monday, January 26, 1998. 8am. To anyone who can help us. We have been abandoned here by the Outer Edge. Please help us or we will die. Tom and Eileen Lonergan."

There has been much debate among experts over whether this find was an authentic belonging or a heartless prank.

The remains of the American pair have yet to be located, and various hypotheses about their fate post-departure from the reef emerged during the investigation and the coroner's inquest that followed. Detective Sergeant Paul Priest remarked at the inquest, some months after the Lonergans vanished, that he initially regarded the diaries found in their hostel as "chillingly bizarre" and "prophetic", but ultimately he wrote them off as the private reflections of a contemplative couple.

The Lonergans' vanishing act served as the muse for the film Open Water, albeit set in the Bahamas rather than the Great Barrier Reef. Striving for authenticity, the director subjected the actors to a harrowing experience to evoke the terror and panic the couple would have endured upon realising they had been abandoned by the boat.

Real sharks were allowed to encircle the actors, and cameras were attached to buoys to capture the drama from the eye-level perspective of the audience. Tuna chunks were thrown into the sea to deter the sharks from attacking the cast.