Actually Hognose snakes only grow to 12 -14 inches and are never that large around. Im still betting it was a banded water snake. Also it's usally water snakes that are in the trees and bushes along the water they like to sun in them and they try to escape when they hear a boat coming,but sometimes don't make it in time!. but even i freak out when i know what it is as me and a buddy were kayaking down the chipola river and were trying to help out some novice canoers who had tipped over. I tied my kayak to a bush and when i returned and went to untie it there was a water snake laying in my seat ,luckily i saw it and after screaming and hollering i looked at it closely and saw what it was and carefully picked it up and put it in my buddies kayak(lol) who's really afraid of snakes and watched him fly off his kayak(sit on top models) and swim down creek with me laughing so hard i almost flipped over. he was okay when i gave him a Budweiser to calm him down .