An interesting "sea serpent" tale

This is from the blog of cryptozoologist Malcolm Smith.  He heard it from a single witness, though the man said he had a companion. It's unusual in that it was an underwater report, of which there are very few, of an elongated marine creature of unknown type.  The witness, Mike Cleary, told Malcolm that he was diving in a bell at some 500 meters depth to look at oil-drilling sites in the early 1990s (This is a point I'll look up - I thought everyone used submersibles these days?)  In any event, Mr. Cleary said a creature some 8m long, elongated, with a dorsal fin like an eel's swam into view. Well, I am one who is of the opinion there is a giant eel or eellike fish behind some "sea serpent" reports, but this report is odder than usual because the animal had two sets of limbs, vs. the single pair of all known eels, and - here's the really hard part - Cleary was insistent these were webbed limbs and not fins.
So there we have it.  Was the witness making it up? Possibly, but it's the other possibility that is more interesting to contemplate - that Cleary saw a real animal. A very elongated pinniped? A freak giant eel with extra limbs?  None of these is very likely, but the sea is a very big place even in the modern world.....