In Over Her Head

She's terrified of the ocean
Marina owner Erica Peck might live near the water, but no way will she ever, ever go in the water. Not since The Incident. But given a choice of facing a bullet or going into the water to retrieve a stolen treasure, she might end up as fish food either way.
He lives under the sea.
Reel Tritone, second son of the king of the Mers has always been fascinated by Humans. As the Spare heir, Reel doesn't have a tail. Or much purpose. But when the devil-may-care ne'er-do-well sees a woman about to become a shark snack, he only has one choice. Even though it's kinda, sorta, totally against the rules to turn a Human into a Mer, even to save her life.
The OMG-OMG-OMG totally naked tailless merman is a hallucination, right? But it's all too real when a death edict sends Erica and Reel on a madcap underwater mission to retrieve stolen treasure from a vengeful ex sea-goddess. Even if they survive, how can they stay together when he's a merman and she's afraid of the water?
*re-release from 2009