If it has a triangle shaped head, it will be venomous. At least in Texas.

It's not clear in the picture but it definitely looks like it has a copper redish tint to it and a pattern on it. The angle of the head is impossible to tell. If the picture wasn't so dark it would be easier to say for sure. With that copper color and pattern I sure have wouldn't get to close.

http://en.wikipedia.org/wiki/Agkistrodon_contortrix

Picture.

Lots found on Google search

I do concur, if you don't know...be careful. Copperheads tend to be shy snakes and avoid people, often slithering away..but they can freeze and hope in camouflage too.

This one was right beside a paved nature trail. Luckily, I was watching the path instead of looking at the birds just then.

Your snake in the picture is a Broad-Banded Water Snake. They are nonvenomous and harmless.

Marti, thanks for introducing me to another Texas snake, and Wayne, thanks for the ID. It seems they are often mistaken for copper heads.

"The harmless broad-banded water snake is a beautiful snake, with broad
bands of olive, black, dark brown, and reddish brown patches separated
by yellowish interstices. Those colors practically scream “copperhead”
to the uninitiated, and even give many, if not most experienced herpers a
start for a second or two when they happen upon one in the wild. It
seems likely that this similarity is another example of Batesian mimicry
(Wickler, 1968) that benefits the water snake by causing it to be
mistaken for a copperhead, and thus to be given a wider berth — sparing
its life — than would otherwise be the case."

More photos of the Broad-Banded Water Snake which certainly seems to try to look dangerous.

I've had another nerodia species,erythrogaster, that freaked my mother out...it spent lots of time in the shrubbery, with head hanging down (waiting), and even lying on the doorstep (warm there in sun).
I had to put my foot down that it was my house and I didn't want to kill the snake. I don't think she was very happy, especially when we heard the leopard frogs it was catching cry out. Hey, it's the balance of nature...and I had frogs almost everywhere.