I don't know much about Texas and Oklahoma snakes -- except you have a lot of less-than-friendly snakes that I don't like very much.
Most of the time, I have no issues with snakes. I try to keep the area around my woodland house less than snake friendly by keeping the lawns mowed low, using snake repellent under crawl spaces, having cats, chickens and guinea fowl, and having a good pest service that keeps my rodent population down. I've relocated a lot of large black racers and black rat snakes over the years that have been sunning themselves in awkward places around the outside of the house. Mostly, they just stray by during mating season.
Snakes by the ponds, and in the woods, come and go. I don't pay much attention to them, unless they have an attitude.
Here in the Virginias and Carolinas we have freshwater snakes like Northern Water Snakes, Brown Water Snakes, etc. I don't particularly care for any of them. The Brown Water Snakes like to sun themselves on tree branches overhanging the water. I'm not sure how many have dropped into my canoes over the years as I've brushed branches on the Shenandoah, Rappahannock, and upper Potomac rivers, but they sure scare the poop out of the human canoe occupants.
I've had a lot more encounters with northern water snakes. Here is a rather old post about a water snake that grabbed my pant leg one morning:
Bad Attitude. It quickly became a two-piece snake.
Most of the time, water snakes just want to get away from people. They are rather anti-social, and don't like anything or anybody, including other snakes, except during mating season and during hibernation, when they will winter-up with copperheads and timber rattlers in our area.
I don't believe I've ever heard of a swimmer being attacked by a non-venomous water snake.
I don't care for most water snakes because they can become quite aggressive under certain circumstances. They certainly eat a lot of live critters, like small fish, tadpoles, and frogs. I can deal with that. But, they are also efficient scavengers. I like that.
However, even though they are not venomous, they have a very toxic mouth due to all the bacteria from the decaying stuff they've eaten. They have a lot of small teeth, and they will bite repeatedly when cornered. Any bite from them should be cleaned out by at a professional medical facility, like an emergency room. They have some other nasty habits when biting, like vomiting the disgusting contents of their last meal. They also can produce some pretty foul liquid poop and they can expel a really nasty musk. Because of that, they are not a critter I like to grab by hand and move to a new location.
As for staying underwater, here is something from
BioKids- Water Snakes Northern water snakes often escape predators by swimming off across a body of water or by diving below the surface, where they anchor themselves to vegetation or logs. They usually remain submerged for about 5 minutes but are capable of remaining below water for an hour and a half.
Just remember,
Be afraid, be very afraid 
