Blue: When The Sea Calls by Ursula Graetz

On the island sanctuary where her Marine Biologist parents run a marine conservancy, Blue sits on the rock, watching as the tides of the sea go in and out, and is tempted to run into the sea, despite being forbidden to do so. But the call of the sea is so strong that finally she succumbs to its lure and runs into the sea. Blue soon discovers her true form and a whole new world that she was deliberately kept away from but which was her inherent right. Secrets, lies, betrayal, murder is the thread that runs through this paranormal thriller.