RC:

... (if I'm not mistaken, this is a Cottonmouth and very poisonous).

1398678807903snake.jpg

It may be, although, I am not herpetologist enough to say definitively from that picture. But, if they aren't hungry and/or are a little cool and are not moulting, and you don't threaten them too much, they are relatively docile. Did it open it's mouth at you? If so, that would have been a good time to back off, and also aids in the identification. They are certainly not uncommon in that area.