This is a Red Bellied Watersnake. It is not venomous, and while watersnakes tend to be aggressive, Red Bellied Watersnakes tend to do a lot of bluffing before they actually bite. This one puffed up, and flattened its head to make it look venomous. It hissed loudly, and made a few "bluff strikes", showing an almost white interior of its mouth in a good imitation of a Water Moccasin. After a couple of bluffs, it quickly turned and disappeared into the grass.
The worst that I risked was a bite on the finger, and with the camera between my fingers and the snake, that was not likely. With that said, I got that close only because I am very familiar with this species of snake, knew that it was unlikely to bite, and I was willing to endure a little pain if I did get bitten.