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Well, a very big eel can not be ruled out, at least.
University of Otago geneticist Prof Neil Gemmell last night announced the findings of his work in the loch.
He travelled to Scotland last year to investigate the existence of the fabled Loch Ness Monster by examining environmental DNA in the waters.
Water samples were taken from the length, breadth and depth of Loch Ness, the DNA from those samples was extracted and sequenced, resulting in about 500million sequences that were analysed against existing databases.
However, the research did not find evidence of Jurassic-age reptiles such as a plesiosaur, one theory of what was behind more than 1000 reported sightings dating back to the 6th century AD.
"We can't find any evidence of a creature that's remotely related to that in our environmental-DNA sequence data."
The research team tested other predominant theories of various giant fish, such as a giant catfish or a giant sturgeon, an eel, or even a shark such as a Greenland shark.
There was no shark DNA in Loch Ness based on the sampling, no catfish DNA, nor any evidence of sturgeon, Prof Gemmell said.
But he could not reject the remaining theory, that what people saw was a giant eel.
"There is a very significant amount of eel DNA.
"Eels are very plentiful in Loch Ness, with eel DNA found at pretty much every location sampled; there are a lot of them."
The data did not reveal their size, but the quantity of the material suggested the possibility there may be giant eels in Loch Ness could not be discounted.
Prof Gemmell said further investigation was needed to confirm or reject the theory.
Loch Ness is the largest and second-deepest body of fresh water in the British Isles.
Prof Gemmell said divers had claimed they had seen eels as thick as their legs in the loch, but he was unsure whether that was an exaggeration.
"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."
He was philosophical about the study findings, and believed no matter what science said, there would always be a belief in the Loch Ness monster.