Fish Out of Water by MaryJanice Davidson

What's on the back of the book:
Mermaid fredericka Bimm has finally made her choice between Artur, Prince of the Black Sea, and marine biologist Thomas - or has she? She's agreed to visit Artur in his underwater home and she's determined to make their relationship work. Why then is she so unhappy? Is it truly Artur who is the right person for her, or could she have made a mistake in her choice of man?

However, Fred doesn't have time to dwell on this - the existence of the Undersea Folk is no longer a secret and someone needs to keep them from floundering in the media spotlight. Fred must do everything she can to help but, as civil war threatens to sink the merfolk, she finds her whole world - and love life - is turned completely upside down . . .

A piece from the book:
The story so far . . .
Fredericka Bimm is a hybrid - her father was a merman who got her hippie mother pregnant one night on the beach and then disappeared forever. Part of both worlds and feeling out of place pretty much everywhere, Fred's dearest wish is to keep herself to herself and stay under everyone's radar.
Circumstances, however, make that impossible. In the last year and a half, she has helped prince Artur of the Undersea Folk (what the mer-people call themselves) figure out who was dumping toxins into Boston Harbor, fallen for a fellow marine biologist (Dr. Thomas Pearson, who writes romance novels on the side), fought pirates (yes, pirates), attended a Pelagic (don't ask), met the king of the Undersea Folk (who is obsessed with the HBO series Deadwood), walked in on her mother and stepfather having sex, walked in on her boss (Dr. Barb) and her best friend (Jonas) doing their impersonation of the Thing That Can't Stop Kissing, visited the Cayman Islands, and watched as several of her father's people showed themselves (tails and all) to the world.
Also, she's taken a leave of absence from her job at the New England Aquarium. So, she's been busy.
Now, six months after the first of the Undersea Folk were seen on CNN, the world is transfixed by the idea that mermaids are real . . . have always been real . . . and there could be one living right next door.
Also, she has to house hunt in Florida. During tourist season.
Oh, the humanity.