I found a spot on the shore of Walden Pond which was unoccupied and jumped in. After swimming across the pond and walking back to my spot I jumped back in to cool off. As I sat back against the smooth boulders the state had sunk into the pond's shore I was bitten by something. Turns out I had invaded the home of a school of juvenile panfish. These guys are fiercely territorial and ravenous. It's a good thing they don't have real teeth.
At one point while picking and eating blueberries from a bush that overhung the pond I noticed a daddy longlegs. I caught the bug and tossed it into the school of fish who promptly tore it to pieces.