Bog Songs. Strains of Portomare, #4

A reluctant leader. A missing friend. And voices from another world. Powerful, gentle Cobi has no idea why he ended up the leader of a team sent to explore a hidden reef, a community living in a hollow rock on Portomare's ocean floor. Yes, he's a strong eldsinger. No, that doesn't make a person a good leader. Case in point: On day one they lose Cobi's best friend, Mica, so the exploration becomes a desperate rescue.
Even worse, this reef floods from time to time, and it seems it's about to flood again. As they search for Mica and answers to floods that shouldn't be possible, they'll struggle to become a team as well as face a wary populace that thinks Cobi and his friends have come to destroy their world. Then they find one simple truth that changes everything they knew about the hidden reefs and the mysterious creatures who put them here.
Cobi didn't want to lead. Now it will take everything he has-and then some-not to lose this reef and his people completely. Bog Songs is book four of the Strains of Portomare series, fantasy about an underwater world and the powerful men and women who travel its currents.