Yes, beavers. They're very efficient an building dams but awful at following engineering instructions, often ignoring them altogether. They make for a very untrustworthy workforce and we should keep an eye on their behaviors especially around critical architecture.
Beavers used to come up from the nearby park, and dam up the lake. They'd chew down the decorative cherry trees (boo), and Bradford Pear trees (yay).
I was reading (maybe here), that beavers basically obviated a multimillion-dollar dam project, somewhere out West.