Have you found this site yet?
http://www.texassnakes.net/pictures.html

There is something on there called a yellow bellied
water snake.

If he shows up again, and you decide to catch him,
I'd take him miles away and to a place where there is
a natural waterway.

Let us know what happens.
As much as I like critters in the pond I'd probably
faint dead away if a snake ever showed up!

kathy :-)