Thats a old one!! Many times explained as a decomposing whale or basking shark.

people are so quick to dismiss it as something common that we all know of, but come on now, it might be what all the others say it is, but we should not count out the fact that it could be some unknown species or some thought to be extinct species. I believe it is something other than a shark or whale myself. But I like to think outside the box on these things...

Unfortunately they didn't keep the corpse.
I'd love to have seen some real testing done on it. It's easy to write something like that off as a basking shark corpse, but that doesn't necessarily mean that's what it is.
I'd love to believe that it's a plesiosaur or something similar...

but we'll never know now.