A Kiwi scientist who has been probing the legend of the Loch Ness monster say there is no evidence the mythic creature exists, though it might be a "very large eel".

With over a thousand reported sightings dating back to the 6th Century, University of Otago geneticist Professor Neil Gemmell said one of the most common ideas was there might be a Jurassic-age reptile or population of Jurassic-age reptiles such as a plesiosaur present in Loch Ness.

"We can't find any evidence of a creature that's remotely related to that in our environmental-DNA sequence data," Professor Gemmell said today.

"So, sorry, I don't think the plesiosaur idea holds up based on the data that we have obtained.

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The research team carried out investigations into the environmental DNA present in the British Isles' largest and second deepest body of fresh water.

They tested other predominant theories of various giant fish; whether it be a giant catfish or a giant sturgeon, an eel, or even a shark such as a Greenland shark.

"So there's no shark DNA in Loch Ness based on our sampling. There is also no catfish DNA in Loch Ness based on our sampling. We can't find any evidence of sturgeon either," Professor Gemmell said.

The remaining theory that Professor Gemmell could not refute based on the environmental DNA data obtained wass that what people had seen was a very large eel.

The loch monster, commonly referred to as "Nessie", supposedly has a long neck and one or more humps that protrude from the water.

Evidence of its existence has always been purely anecdotal, with a few disputed photographs and sonar readings.

Popular interest and belief in the creature has varied since alleged sightings came to worldwide attention in 1933.

Professor Gemmell said further investigation is needed to confirm or refute the eel theory, "so based on our data, giant eels remain a plausible idea".

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In 1933 researchers had also proposed that a giant eel might be the explanation for some Loch Ness sightings. That idea then waned as notions of extinct reptiles became more prominent.

Professor Gemmell noted other evidence such as the video shot by Gordon Holmes in 2007 which showed a 4 metre torpedo-like shape seemingly swimming on the Loch's surface supported the hypothesis of a giant eel, large fish, or perhaps a marine mammal.

"Divers have claimed that they've seen eels that are as thick as their legs in the loch, whether they're exaggerating or not - I don't know - but there is a possibility that there are very large eels present in the loch.

"Whether they are as big as around 4m as some of these sightings suggest – well, as a geneticist I think about mutations and natural variation a lot, and while an eel that big would be well outside the normal range, it seems not impossible that something could grow to such unusual size."

Professor Gemmell was philosophical about the study findings, and believed no matter what science said, there would always be belief in the Loch Ness monster.

The new findings came several years after the idea of turning new science toward the myth was first mooted on Twitter.

Darren Naish, the author of a book called Hunting Monsters, used the platform to quiz Professor Neil Gemmell on whether environmental DNA, or eDNA, might be the key to clearing up the mystery.

Environmental DNA, capable of uncovering a wealth of information with just a single water sample, seemed an obvious solution.

Gemmell got an email from John Paul Breslin, a Scottish journalist , asking whether they'd ended up progressing the idea. Though the answer was no, it was still enough to give Breslin an article that quickly spread across the Scottish press - then around the planet.

The response stunned Gemmell.

Professor Neil Gemmell of Otago University has been hunting for the Loch Ness Monster. Photo / Supplied
Professor Neil Gemmell of Otago University has been hunting for the Loch Ness Monster. Photo / Supplied

"In fact, we would have got more publicity out of just saying we'd decided not to do anything at Loch Ness than all of the other work my team had done put together - it was crazy," he told the Herald last month.

Not long after that, Gemmell found himself on a boat in Loch Ness, collecting hundreds of samples from various parts of the lake, some from as deep as 200m.

Choosing to pursue the project obviously posed a potential risk to his scientific reputation, with some colleagues suggesting the idea could be a career-killer.

Professor Neil Gemmell (third from left) with his team out on Scotland's Loch Ness. Photo / Supplied
Professor Neil Gemmell (third from left) with his team out on Scotland's Loch Ness. Photo / Supplied

Yet he also understood that doing science was just one part of a scientist's work; sharing and communicating it was another.

"I felt like for 25 years of my academic career, I'd only just realised how I could be smart about it."