I think etrrel is way to far from the range of the brazos water to be one, looks like a diamondback water snake to me, N. rhombifer rhombifer, but until i get home and look at a field guide i wont say for sure, I can't remeber how the belly should be marked and dont want to look it up. The other one i was thinking was brown, N. taxispilota, but I don't think thats it.