Could be an urban myth warning.
Back when I lived in Pontywaun and knew the boys in Martin Hatfield well there was the tale of a group of lads riding up the canal from Risca to where it stops in Pontywaun to go up the Scenic Drive, the one at the front ran over a fishermans kit and the one at the back paid fot it by being given a beating by the angry angler. He and his bike ended up in the canal.
If you spent the night on a canal bank only to let go what you had spent hours trying to catch I think you would be a little unglued.