Drowned (Drowned #1) by Nichola Reilly
Coe is one of the few remaining teenagers on the island of Tides. Deformed and weak, she is constantly reminded that in a world where dry land dwindles at every high tide, she is not welcome. The only bright spot in her harsh and difficult life is the strong, capable Tiam—but love has long ago been forgotten by her society. The only priority is survival.
Until the day their King falls ill, leaving no male heir to take his place. Unrest grows, and for reasons Coe cannot comprehend, she is invited into the privileged circle of royal aides. She soon learns that the dying royal is keeping a secret that will change their world forever.
Is there an escape from the horrific nightmare that their island home has become? Coe must race to find the answers and save the people she cares about, before their world and everything they know is lost to the waters.