This actually happened last night. Was fishing with my cousin in a local pond. We put our float tubes in the water on one end of the pond and started fishing down the bank to the other side of the pond. We fished for about 2 hours and started heading back to where we put in. We saw something swimming about a hundred yards away and couldn't really tell what is was. It went under water for a few minutes and resurfaced about 20 yards from our tubes and........wait for it.......WHAMO! It slaps it's tail on the water! It was of course, a beaver. Being scared out of my mind and not wanting to pee in my waders, I took off back toward the other side of the pond. No way was I messing with that thing. My cousin is a little harder headed than I am, he just kept right on going. He get's about 40 feet from the bank and......wait for it......WHAMO! Two very angry beavers! They were both around 40-50lbs.They circled around him within two feet of his tube slapping their tails over and over, so close they were splashing him. He went ahead and followed my lead and took off to the other side of the bank. It was a pretty scary experience, I can't stop laughing out it though! I heard beavers are pretty docile if not provoked, I really didn't want to take the chance.....