Early in the movie, when Samantha and Javier meet at the bar, and then walk to his boat, they talk about there being a full moon that night. A full moon is then shown in the sky. Later, a wide shot of the resort hotel shows a sliver of a moon in the sky the same evening, right before the daughter, Ellie, goes looking for her mother.
At the beginning of the movie, a drugged girl falls backwards into the water right at the shoreline and sinks deeply into the ocean. People float and the barrier type island has gently sloping shores. A body would not disappear a few feet off a sandy beach.