What kind of snakes do you think these are? (north texas, blackish brown small snakes)?

You live in Dallas, correct? I live in Arlington. What you are seeing are blotched water snakes, completely harmless. Many people assume that every snake they see in the water is a water moccasin (aka cottonmouth), but they are rare here in DFW. Blotched water snakes and diamondback water snakes are abundant here. Although harmless, they are aggressive and have a nasty smelling musk.