That is a diamond backed water snake. The bacteria in their mouth makes their bite very infectious and just as dangerous as a cottonmouth.
IMO, It does look like a Diamond Backed water snake due to it's markings on the back and belly. They don't look like the bands you'd see on a Banded or Broad Banned Water Snake. The colors match that of a Diamond Back Water snake. The only thing is, I never heard of is any water snake being just as dangerous as a Cotton Mouth. Don't get me wrong, most reptiles have some sort of bacteria in there mouths, water snakes included, but I didn't think it was THAT bad. Now if it were a Kamodo Dragon, that is a different story. You'd for sure need to go to the doc about that bacteria. I'm am sure not an expert...so I may be wrong. Just my opinion. Over all, just don't get bit. haha