It is one of the British Isles' most enduring legends that somewhere in the deep dark waters of Loch Ness lurks a prehistoric monster.
While some dismiss it as foolish nonsense, fabricated to boost the tourist trade, it is a claim which has prompted serious scientific research on several occasions. On October 11th, 1987, the results of the latest serious search for Nessie were unveiled, but the news was disappointing for believers in the beast.
For the week-long "Operation Deepscan", specialist naval detection equipment worth more than a million pounds was used to scan the deep freshwater loch from one end to the other. A flotilla of 24 boats was used in the search, but they failed to find any convincing evidence of Nessie's existence.
They did pick up three sonar contacts which indicated something of a reasonable size in the waters below Urqhart Castle, but investigators conceded they could have been a seal, a submerged log or even a shoal of salmon.
Project leader Adrian Shine, who had been looking for Nessie for many years, said: "I think if we were to get a fish on the scale that the contacts would suggest, then I don't think anyone would be too dissatisfied and all those eye-witnesses would get their vindication."
The legend of Nessie goes back as far as the sixth century, but it was only from the 1930s that it gained national and then international momentum. One day in 1933 Mr George Spicer had been driving along the loch side with his wife when they claimed to have seen a monster some 50 feet long slither across the road ahead of them, making for the water.
Mr Spicer told newspapers: "Although I accelerated quickly towards it, it had disappeared into the loch by the time I reached the spot. There was no sign of it in the water. I am a temperate man, but I am willing to take any oath that we saw this Loch Ness beast. I am certain that this creature was of a prehistoric species."
As technology enabled the story to spread around the globe, more and more people came to Loch Ness in search of the monster, leading to more claimed sightings, and so the legend grew. Soon a lucrative tourist industry began to build up, with the mythical beast featuring in magazine articles, novels and even feature films.
Most witnesses describe the monster as having a long neck, a humped back and large fins, similar to a plesiosaur – a marine reptile from the age of dinosaurs. There have also been various photographs and even film footage purporting to show Nessie in the loch, but almost all have been later discredited as hoaxes, some elaborate, some incredibly simple.
Yet even in the face of so many hoaxes, the slim possibility of a monster in the loch continues to intrigue scientists and serious researchers. There have been several other intrepid and well-equipped Nessie hunting expeditions since 1987's Operation Deepscan, including one in 2003 using 600 separate sonar beams, the latest satellite navigation technology and filmed for the BBC. Once again, it drew a blank.
One thing's for sure, if an underwater prehistoric monster was looking for somewhere to hide, it could do a lot worse than Loch Ness. At 23 miles long and more than 750 feet deep, it contains more fresh water than all the lakes in England and Wales combined. A high peat content also means its deep waters are extremely dark and murky, with exceptionally low visibility.
So who knows, maybe there's a whole colony of Nessies down in the loch just waiting to be discovered?