Professor Henry Bauer’s research found that Nessie may be a type of undiscovered turtle trapped in the Loch as the waters receded at the end of the last Ice Age.
A self-confessed Nessie fanatic, US scientist Buaer also rubbished the idea that Nessie is a form of dinosaur.
Henry, 89, a retired professor of chemistry and science studies at Virginia Polytechnic Institute and State University, said: “The most popular idea is that the Loch Ness Monster has a relationship to extinct plesiosaurs.
“But this is difficult to square with the rarity of surface sightings, let alone occasional sightings on land.
“On the other hand, everything described for the Loch Ness Monster squares with is known many living and extinct species of turtles.
“They’re air-breathing but spend very long periods in deep water.
“They venture onto land, are very fast in water, have the ability to be active in very cold water and have relatively long necks.”
Professor Bauer’s work – which has been published in a respected scientific journal – is the latest chapter in a global fascination with Nessie.
One of Scotland’s oldest myths, reports that a creature was living in Loch Ness date as far back as the 6th century.
The first written account was recorded in 565 A.D. in a biography of St. Columba.
According to the text, the creature bit a swimmer and was prepared to attack another man when Columba intervened.
He ordered the beast to “go back” and it obeyed.
And in 1960, aeronautical engineer Tim Dinsdale filmed a hump that left a wake crossing Loch Ness.
Possibly the most famous ‘picture’ of Nessie was from 1934, however it was soon debunked as a hoax.
The elusive monster was “seen” 12 times last year. In December, a couple visiting the loch said they saw a creature repeatedly surfacing.
The news came weeks after a boat’s sonar picked up a 33ft object 550ft down.
At the time, Gary Campbell, of the Official Loch Ness Sightings Register, said: “It all adds to the mystery. In many ways it is a vintage year for sightings.”
And Professor Bauer backs the claims, saying he is sure the Monster was real having once joined an investigation into the beast.
He said: “Tim Dinsdale’s film taken in 1960 is the conclusive proof, but there are also innumerable contacts by sonar, some excellent underwater photographs, and a few plausible surface photographs.
“I became seriously interested after seeing Dinsdale’s film, and 26 years later was an observer at Loch Ness during Operation Deep Scan, when a whole fleet of boats made a sonar search for Nessie.”
“Everything points to creatures that spend most of their time in the deepest parts of the Loch.
“None of the evidence supports the idea that these are monstrously large eels.”
Professor Bauer also revealed he is a big fan of Scotland’s more genuine attractions – especially a full Scottish breakfast.
He added: “I love Scotland, including Tartan beer and in my younger years, full traditional Scottish breakfast.
“In 1958 I had a honeymoon tour of Scotland during two weeks of superbly fine weather.
“We saw the marvellous scenery to the north of Inverness, took a trip past Loch Ness (without stopping to see Nessie).”