Sure, there are sophisticated cameras that work under water but those are handled by professionals, not by tourists on their honeymoon. By definition, a "selfie" is taken by smartphone or webcam.
Also, that water is way too clean to be in the ocean. This is obviously a professional photo taken in somebody's pool with an underwater camera - the shark and fish were then photo-shopped in.
Uh, my Galaxy 5 is waterproof.