The only one I've ever seen flashed its white mouth at me from a face-level tree branch about 10 feet away while I was paddling front position of a canoe in a little stream in the Ozarks. I paddled hard in reverse and yelled "reverse", my partner did not and just yelled "what?" - so I whacked it with my paddle and beat it to death on the water with repeated paddle smacks. It was probably just being defensive, but I don't regret killing it.
I do like snakes, even the other venomous North American species - but even before that encounter I disliked cottonmouths, and that never changed.