The long-necked creature, which resembles a supposedly-extinct plesiosaur, was supposedly stalking and snapping at fish, which were so terrified that they ended up beaching themselves.
The mystery creature was also photographed by Gill Pearce as it followed a shoal of fish at Saltern Cove in Paignton, Devon, on July 27.
Gill reported her sighting to the Marine Conservation Society where it was studied by sea life experts.
The UK is home to probably the world's most famous cryptid, the Loch Ness Monster.
Mystery "sea monster" seen
Terrifiying ... experts baffled by 'sea creature'
By STAFF REPORTER
30 Jul 2010
A MYSTERIOUS Loch Ness type creature has been snapped stalking fish - just YARDS off the British coast.
The fish were so terrified they beached themselves just seconds after the long necked creature was snapped speeding towards them.
The strange Plesiosaur-like creature was spotted just 30 yards off the Devon coast by locals who reported a sighting of what they first thought was a turtle.
But pictures taken by one of the baffled witnesses reveal its neck is far too long for any known sea turtle.
Extinct? A plesiosaur.
Experts are totally baffled by the sighting.
Gill Pearce photographed the creature following a shoal of fish at Saltern Cove in Paignton, Devon, on July 27.
She at first thought it was a large sea turtle but baffled experts say it doesn't fit the description because the greenish-brown beast with a small reptile head has too long a neck.
Mrs Pearce reported her sighting to the Marine Conservation Society where it was studied by sea life experts.
"Gill Pearce spotted the creature about 20 metres from the bay at Saltern Cove, near Goodrington," said Clare Fischer from the MCS.
"It was observed at about 15.30 on 27 July but by the time she had got her camera it had moved further out.
"She spotted it following a shoal of fish which beached themselves in Saltern Cove.
"The creature remained in the sea, then went out again and followed the shoal - this indicates it's not a turtle as they only eat jellyfish.
"We would love to know if other people have seen anything like this in the same area and can help clear up the mystery."
Some people think the sea sighting could be linked to that of a sperm whale sighted off south Devon recently but Clare thinks not.
"They [sperm whales] wouldn't come that close inshore and the reptilian-like head counts that out - at least that's what the experts are saying!"
The sighting has caused a stir on the MCS website too where theories range from sea serpent to salt water crocodile.
An MCS spokesman said: "It was reported as a turtle as it had large front flippers and small back flippers and what appeared to be a shell but was also said to have a small head on a thin neck about two-feet long which craned above the surface like a Plesiosaur.
"It's described as being as long as a sea lion with a long neck which floated at the same height in the water all the time."
"This is not a fake
"The problem is the distance and clarity from which the photos were taken.
"The lady thought it may have been a turtle - but turtles don't chase fish."
"It was reported as a turtle as it had large front flippers and small back flippers and what appeared to be a shell.
"But it was also said to have a small head on a thin neck about two feet long, which craned above the surface like a Plesiosaur.
"No sea turtles do that with their heads and we do not know of similarly described freshwater turtles that grow so big.
"So at the moment it is 'unidentified' - the person who reported it has trawled the internet and says the closest ID fit is a giant green sea turtle - but the description of the head doesn't add up."
The organisation has now asked for people to keep a keen watch on the seas off South Devon and appealed for more photos to be taken, adding: "If you live or are visiting down near Saltern Cove Goodrington, near Paignton please keep your eyes on the sea and let us know if you see anything - and keep your camera by your side just in case.