I too had beavers living in excavated dens in the bank of my pond, and in addition to felling trees, they dug up a bunch of lily pad rhizomes and used them along with sticks to clog my drain pipe. They needed to tunnel under my pig-panel trash guard to get to the pipe, so they were only able to get a few larger sticks through to the pipe. I had no idea that we had a half dozen beaver until the neighbor trapped them out.
