There ore only 4 poisonous snakes in the USA. Water moccasin (cotton mouth) which is the most common in the south. 95% of them look almost black with a band across their eye like a raccoon. The younger ones can vary from brown to black with bands across their body. They have a very short and fat body. There are a couple of water snakes that people get confused with the water moccasin all of the time. They are harmless but they are mean as hell and they have a very distinct odor and are alot longer than most moccasins.

The rattle snake is going to be almost nonexistant in swamps.

You might run into a copperhead but they are no where near as poisonous as the other two and is about like a bad bee sting.

The corral snake you will probably never see and don' t have to wory about one biting you cause they do not have fangs like the other three. I have never seen one in the wild and I have looked for them.

If you see a moccasin and are worried about being bit the best thing to do is just leave it alone.

Here is a link to snakes found in Arkansas you might find useful.
http://community.webshots.com/album/14412881PHgKixOgZd