Forbidden Sea by Sheila A. Nielson (Published by Scholastic, July 1, 2010)
Adrianne is struggling with the harsh reality of poverty in her seaside village, only to be swept away to an underwater mermaid kingdom to be the bride of the Prince of the Sea. Chosen for her noble heart and character, Adrianne realizes that she has not seen herself clearly for who she is--someone who could be a princess. She must make a decision: embrace this strangely luxurious life under the sea, or return home to the ones she loves and the difficulties ahead..
I love the premise of this book! An underwater mermaid kingdom sounds so cool, and the cover is so pretty. I wish the release date for this one wasn't so far off!