Paleontologist Dr Darren Naish reckons there have been too many sightings for 'Nessie' to be a hoax.
Boffin Dr Naish, who lectures at the University of Portsmouth, said: "The huge number of 'sea monster' sightings now on record cant all be explained away as mistakes, sightings of known animals or hoaxes.
"At least some of the better ones some of them made by trained naturalists and such probably are descriptions of encounters with real, unknown animals.
"Because large marine animals continue to be discovered various new whale and shark species have been named in recent years the idea that such species might await discovery is, at the very least, plausible."
Some experts reckon Nessie is a plesiosaur - a long-necked reptile that lived at the same time as the dinosaurs.
But Dr Naish and another dino expert dismissed this idea in speeches at a conference, 'Cryptozoology: Science or Pseudoscience?', in London.
Dr Charles Paxton, of the University of St Andrews, said: "If there are prehistoric animals alive today it would imply that theres something very wrong with our understanding of the fossil record."
Dr Paxton added it could not be assumed all large animals living in the oceans have been discovered.
He said: "If the criteria is solely bigness, then this is not the case.
"In 1995 a benthic ray, which lives on the ocean floor, was found that measured 3.42 metres and eight large marine species have been discovered in the past 20 years."
Cryptozoology is the study of hidden animals or the search for creatures whose existence has not been proved.
There have been hundreds of 'sightings' of the Loch Ness monster since 1933 in the lake, which is 22.5 miles long and up to one-and-a-half miles wide and 754ft deep.