Some vandals let all the water out of the Kennet and Avon canal near Thatcham a few years ago (this is actually quite hard to do, as most of that section is a canalised river, so, unless you can work the river sluices as well as the lock paddles, you have to drain a pound with no river ingress/egress between locks). Luckily, narrowboats don't have a keel and will just sit in the mud. A bit annoying, though.