The Dark and Deadly Pool — Joan Lowery Nixon

For fans of Gillian Flynn, Caroline Cooney, and R.L. Stine comes The Dark and Deadly Pool from four-time Edgar Allen Poe Young Adult Mystery Award winner Joan Lowery Nixon.
 
        Liz enjoys her summer pool job at the glamorous Ridley Hotel. Until the dark and lonely night when a ghastly shadow surges up from the pool. A face -- eyes wide, mouth gaping -- stares at Liz. A hand clutches at her sneaker. Then it, whatever it is, is gone.
        But danger isn't. Strange things are happening at the hotel, and a shaken Liz wants to know why. But whoever is behind the trouble will stop at nothing -- not even murder -- to get what he wants.
 
“[A] suspenseful mystery, rounded out with touches of humor and romance.” �"Publishers Weekly