Lived on Cow Bayou near the Texas/Louisiana border growing up .... poisonous snakes swim .....
Yes, and cotton mouths can bite under water, as well. What I hate about cotton mouths, is their willingness to drop out of a tree into your boat all the while copping an attitude...little load of ratshot deals with that attitude though.
Largest rattler (timber rattler) I ever killed was lying on the bottom of our duck pond about 6 inches deep. After that first .22 cal hit him he swam for the opposite side bank...it was a fiasco getting him dead, ran out of shells, broke my stock on him, nearly got bit, finally got a shovel on his head...ended up being 7'3" without his head and 5" of neck.