Looks to me like a harmless & beneficial prairie king snake (Lampropeltis calligaster) but can't be sure with that photo.
Not seeing the whole snake...there's other possibilities too, like a cottonmouth or a water snake. I'm not exactly sure
what water snakes are in your area, but they often resemble cottonmouths & get killed for that mimicry.
check this out: http://timberrattlesnake89.tripod.com/midlandwater.html
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