The Changeling Sea - Patricia A. McKillip

World Fantasy Award winner Patricia A. McKillip tells "an enchanting fantasy that is tinged with realism and romance." (School Library Journal)
Since the day her father's fishing boat returned without him, Peri and her mother have mourned his loss. Her mother sinks into a deep depression and spends her days gazing out at the sea. Unable to control her anger and sadness any longer, Peri uses the small magic she knows to hex the sea. And suddenly into her drab life come the King's sons—changelings with strange ties to the underwater kingdom—a young magician, and, finally, love.
"McKillip is a master storyteller; her tale rings true as if it were being told from memory."—Kirkus Reviews, pointer review