My family's been waging war on beavers down on the farm for over 40 years now. Sometimes, after some losses, they leave for a few years, but they always come back. A game warden told me that they don't reproduce every year, and the young, once they mature, leave to build their own ponds elsewhere. They do make a mess. I've shot some that must have weighed around 40 or 50 pounds, once fished out of the water. We prefer something with a bit more whomp than a 22 though.