Not seen this before

Out walking my dogs as usual and noticed this in part of a river I don't normally walk to and wondering what it is/was.
Looks like been it's been there a while as it looks odd/old.
Any ideas as to what it could have been I think possibly out of the old Isle of Skye Woollen Mill closed for years now, maybe.
I uploading a thumbnail of the end of it in close up might give an idea of what it is/was.
Answers on a postcard ;0))