A scientist has spent four painstaking decades studying the loch best known for the creature affectionately known as "Nessie". Why does this mythical monster hold such fascination for so many people, ask Chloe Hadjimatheou and Vanessa Barford.
Adrian Shine has patrolled lakes by day and night. He's taken countless photos, and he's used all the latest technological advances in sonar to uncover the mystery behind Loch Ness monster.
Twenty-five years ago this week, he led what was at the time considered the most extensive search of Loch Ness - a £1m exploration called Operation Deepscan.
The week-long project consisted of a flotilla of 24 boats, equipped with high-tech sonars, which trawled the 22.5-mile (36km) long, 738ft (227m) deep lake in the Scottish Highlands for two days.
Shine may have gone to unusual lengths in his hunt for the Loch Ness monster, but he is far from alone in falling under its spell.
Willie Cameron, an expert on the Highland tourism market, says about one million people visit Loch Ness and the surrounding area every year, with the value to the economy worth about £25m.
And he says more than 85% of them are attracted by the phenomenon of the Loch Ness monster.
"Loch Ness has become a brand as big as Elvis Presley, Madonna and Coca-Cola - but by default rather than design," he says.
So when did the Loch Ness monster gain such mythical status, and what is the fascination with finding it?
Jonathan Downes, director of the Centre for Fortean Zoology, says the legend of the monster dates back to the 6th Century, but it was not until the 1930s that it really took off.
Since then there has been a flurry of sightings, with more than a thousand people insisting they have seen creatures in Loch Ness.
Most descriptions of encounters lend themselves to either the theory of a multi-humped sea serpent or the plesiosaur, a long necked dinosaur from the early Jurassic period.
"People like to think of it as a giant prehistoric reptile living in a lake, but it can't be, that's nonsense.
"But it's a lovely notion. I think people find the idea of a 21st century monster, a prehistoric survivor, irresistibly romantic," says Downes.
Downes says the odd thing about the Loch Ness monster is that although it is "the most iconic mystery creature", it is actually the one with the least amount of evidence of its existence.
So-called physical evidence has turned out to be hoaxes, he says.
"Footprints turned out to have been made by a stuffed hippo or stuffed elephant, and a 'monster body' that washed up in 1972 turned out to be a dead elephant seal," says Downes.
So most of the legend around what lies in Loch Ness comes from stories and sightings.
And Shine has first-hand experience of how unreliable they can be.
He says shortly after he arrived in Loch Ness in the 1970s, he rowed out on a nearby lake, Loch Morar, which has its own history of monster sightings, hoping to spot something.
"Suddenly there it was - the classic profile of a large hump and then I saw a half-submerged head which seemed to be moving," he says.
He excitedly began snapping pictures but soon realised that it was nothing more than a strange-shaped rock sticking out of the water.
"That was when I realised that if I couldn't trust my own eyes I shouldn't necessarily trust anybody else's," he says.
Nevertheless, Shine says it is hard to dismiss "the honesty and volume" of eyewitness testimony of the Loch Ness monster.
Lots of locals, too, believe there is something lurking in the loch, according to Cameron.
"I know four people who very genuinely believe they have seen a creature, but they would not speak about it publicly for fear of ridicule.
"My late father saw something unexplainable on 15 June 1965. Nine other people saw it at the same time - and it had a power source because it went against the wind. He said describing it would be like trying to describe a tomato to a blind man."
Operation Deepscan picked up three large unexplained sonar "contacts". They appeared on the scanners as crescent shaped marks - which some people believed were too big and too deep to be any creature known to inhabit the Loch.
However, others say the "contacts" could have been a seal or a group of salmon.
But Shine, who now runs the Loch Ness & Morar Project and is still hoping to find out what is behind the mystery, says the beauty of the monster myth is that no one can disprove it, short of draining the loch.
Although he doesn't believe that Scotland's most famous and reclusive resident is a dinosaur, his own theory is that it is a "Jurassic creature" of sorts.
"I think it could be the occasional navigationally challenged Atlantic Sturgeon," he says, with a mischievous smile.
Known to grow to over 4m long, the fish, which has reptilian scaled plates along its back and a long pointed face with tusk-like barbells hanging from its jaws, is not indigenous to Scotland. It could conceivably make its way up River Ness and into the loch in the search for new breeding grounds.
"It could very easily have swum into the loch, been spotted and left again leaving nothing behind save an enigma," he says.
Of course theories are part of the appeal for many intrigued by tales of the Loss Ness monster.
Downes says the only theory that makes sense to him is that a "gene of gigantism" might have created an eel that was bigger than normal.
Cameron, on the other hand, says the sightings could be a number of things, including a large, nocturnal invertebrate, or a large seal, shark or dolphin that has come in from the sea.
But Shine says even if he does manage to prove his theory about the sturgeon, he is under no illusion that it will bring an end to the mystery of Nessie.
"If Operation Deepscan proved one thing, it is that you can't kill a legend with science," he says.
Cameron concurs: "This fascination with the Loch Ness monster is now part of the public psyche. Everybody loves a mystery."