I've had more experience with cotton mouths. I can attest to their agressive nature too. Case in point:
When I was a kid my thing was rooting around in the woods. We lived in the country outside a small town, Rayne LA, that was good for a boy like me. My friend and buddy in the Boy Scouts, future best man at my wedding, Dane, hung out with me a lot in those woods. He had a .22 pelet gun, but was the worst shot in the troop.
Anyway one day we were hiking in the Louisianna woods, and got to the bayou. Our plan was to wad across as usual, but there was this newly fallen tree that went right across. We decided to stay dry if we could, so I started across. The tree wasn't big, roughly 10" diameter at the base. Maybe halfway across a snake pops up under my feet. I had a stick and clunked it in the head. Two steps later that tree gave a crack and I took a header. Suddenly I was chest deep in that muddy Louisianna water.
Unfortunately the spot we usually waded across was farther upstream, and those muddy Louisianna bayou banks aren't conducive to climbing, so I couldn't get out. Then up comes that snake, and starts moving at me like it meant business. I thought I was a goner. I was certainly about to be bitten in the face by a cottonmouth. I remember thinking it was the biggest I'd ever seen. Closer and closer it came while I was struggling to climb the slimy mud bank. Giving up I turned and planned to use my stick. Before I had a chance Dane shot and hit that moving snake right in the head. It was maybe 3 feet away from me when that happened. Probably the best shot he had ever, or will ever make. Needless to say I had quite literally sh*t my pants. I remember being very happy when they hauled me up out of that water. We did skin that snake and tack it to a piece of plywood. Later that summer I saved Danes ass from a copperhead that was literally coiled around his leg. He had practically stepped on the thing. Lucky for him I was a pretty damn good shot and cleanly removed that snakes head completely missing his leg. It was only a two foot long snake, and a copperhead is nowhere near as menacing as a cottonmouth, but we were both just as grateful when it was dead. Beautiful skin too.