Just talked to the witness Steve Jenkins on BBC Radio. He saw the beast at around 11.30 on Sunday from a distance of 3-4 m.
He is a fisherman so not likely to confuse it with a fish.
So little chance of a mistaken identification. He saw it had 4 legs, long tail, dark colour.
Sounds like a croc of some type to me. More as it comes in. Will meet him later.