Glad to hear the pup's recovering. Like stated previously, I too would rather get bitten than a good fishin' buddy.
As for the swimmin' snakes, i belive most snakes in the US can swim to some extent. According to most books i've read regarding snakes, I can't recall ever encountering a species that was completely hydrophobic (some just prefer water more than others). I spooked a racer a couple of weeks ago that shot across the water like it was the wind.
Elkmont must be a rattlesnake gold mine. last year, myself and several other onlookers watched as a good-sized rattler swam across the stream (towards us on the trail). it crawled onto rocks when it could, but put on a decent display of aquatic mobility (didn't appear to like the ordeal, though).