We used to call those "mud puppies". They are harmless and almost cute. They seem to be pretty scarce here in Louisiana, as I have only seen 1 or 2. Maybe they are just hard to spot because they're nocturnal.
Here in Cajun country, we have plentiful "mud eels" (They are in the order amphiumidae). I have seen them nearly 30" long. They are very strong and quick, and have powerful jaws. After poking one with a stick and seeing how hard they bite, I keep a respectful distance. The locals believe they prey on crawfish by burrowing down into their holes. The red and black mud snake in turn burrows down into the mud eel's holes and feeds on them. All that burrowing makes me a little nervous about my levees, but I think I'm safe with over 12' thick.
Edit: Found a picture. Not a pretty sight.
http://www.enature.com/fieldguides/enlarged.asp?imageID=19335
