I don't know of cases for tablets like that, just pouches. You won't be able to use the screen underwater, though, and some might even prompt weird 'touch inputs'.
I use one with my tablet while on the tub or the jacuzzi to read or watch movies, but if too much water gets on the screen or if I submerge it, I get all kinds of weird screen inputs and using it becomes impossible until I wipe the water off the screen.