I cannot identify it but I've been told that if the head is triangular shaped that it indicates a poisonous snake.

Edited my post because I have no idea lol! My snake field guide is in my backyard and there is no way I'm going out after dark to get it.

I would check out water snakes. It looks non venomous.

Brown watersnake ...

Round pupils, rounded snout, no "pit" = some sort of watersnake.

Coloration differences ... yours has mismatched blotches and a striped tail all the way down - brown water snake.

I think you're right; I zoomed in very close on the photo and it seems to match what you are saying. It disappeared from the yard; probably slid back into the lake. Thanks!

They WILL bite if you grab them ... more of a problem, they release an amazingly stinky fluid as a defense.

But they are good vermin control.

I told the kids to just assume all snakes will bite, even if not venomous, so they don't have to try to figure that out. Since we are on a lake I'm sure we get vermin up in the yard. We have 2 dogs which do scare away a lot of critters, but I appreciate the snake helping out. I am scared of moccasins, so whenever we have those we call a guy to come trap it. He's a naturalist and doesn't kill them, but he takes them far away from me! I didn't want to bother this snake if it isn't venomous, so thanks for all the help!!

This isn't a Brown Watersnake. Brown Watersnakes don't occur west of the Mississippi.

This is the somewhat similar looking Diamondbacked Watersnake (Nerodia rhombifer). They are very common in SE Texas. (This one is a bit paler than your because it is from further west in Val Verde County.)

They are harmless, but they can bite if they are afraid or feel under attack (as would your dogs). Just leave it alone and it will move on back to the lake edge where it has lived for years without negatively impacting you or your neighbors.

The triangular shaped head "rule" doesn't work because lots of completely harmless snakes have triangular-shaped heads (when seen from above) and many harmless snakes that don't normally have a triangular head will flatten their heads out when scared, making them triangular looking.

Here's a completely harmless Texas Nightsnake flattening its head out to look scary, even though it is completely harmless -

Second what fhfchrish already said-harmless Diamondback Water Snake(Nerodia rhombifer). This is a very common and often-large snake found in TX. Like the Brown Water Snake, they have slightly "bug" eyes that are situated almost on top of the head, in contrast to the eyes of a Cottonmouth, which are down on the side and have a flattened scale that protrudes out over the top of the eye like a visor(and serves the same purpose), so that the eyes can't be seen when the head is viewed from above, especially from behind the head. NO snake, including venomous species, are just going to charge up to someone and bite for no reason. Snakes bite only when they feel threatened and have no means of escape, and some won't even bite then. Water Snakes have a bad reputation for being quick to bite if grabbed or picked up, but I've found that if handled gently, most will not bite at all and become tame very quickly. A Water Snake bite doesn't hurt, but it will bleed quite a bit due to anticoagulants in their saliva, and that seems to have a positive effect of flushing out any bacteria, but again, you have to corner and grab or hurt the snake to get it to bite.

eyes of a Cottonmouth, which are down on the side and have a flattened scale that protrudes out over the top of the eye like a visor

Yes, the scowling look (see the comparison pic above).

The pupils are a bit tricky, because getting close enough to look deeply into the eyes of a possibly venomous snake ... bad idea.

Thanks guys! So we have had at least 3 of these snakes in our yard in the last month (after having only 3 in the previous 17 years!). I was trying to figure out why and I think it's because I have been clearing a lot of brush, vines, dead shrubs and trees, roots and such from one side of our property over the last several weeks. I was over there today finishing up, and it seems like it would have been a nice snake home before my clearing. They were probably just displaced and slithering around wondering where their home went. I don't mind having them around if they help with rodent control, but I just don't want to step on one.

Water Snakes do not normally eat rodents or other warm-blooded prey unless tricked into doing so by rubbing a rodent with their favorite food-FISH. They are fish and amphibian eaters, and some species(like the Brown) specialize in small catfish, such as bullheads and mad toms. Rodents probably would still recognize their presence as SNAKE, though, and avoid areas where they hang out.

LOL, Sharon, "derpy" expression is spot on!

The comparison pics are GREAT!