20 years ago you could catch the odd piranha and angelfish from the Grand Union canal at West Drayton where the cement works pumped hot water into the canal, no idea how they got there but there were rumors of a pet shop going bust, though i find it unlikely that the fish just happened to find the only warm spot in miles and miles of canal, they were much more likely to have come from someones tank on the nearby housing estate. Just like in the post above the cement works closed and the unusual fish disappeared with it.