The only waterproof case I know of is the Lifeproof, and even though Otterbox bought them in 2013, they still only make cases for iPhones.
Read Oh, no! My Phone got Wet! - search for the words "on a boat". I've taken a phone down as far as 10 feet that way. Or look at this Amazon page if you want to spend a few dollars.
Test anything you decide to use in a sink first, then in a bathtub. If it leaks in there, you can get the phone out fast. (Just look for bubbles.)
I ended up purchasing a CaliCase pouch and it worked perfectly! Even got some underwater shots. Highly recommend for anyone looking for extra protection for their phone when in the water.