The Dark, Dead, Deep by Michaela Haze

Lady Maeve Cruinn will never take the High Throne. Her uncle has made sure of that.
All she has to do is keep her head down,
make the migration and the offering to the Gods,
and all the magic she could wish for will be hers.
When the Migration goes wrong, and Maeve gets caught up in the decade-long war between the Undine and the other creeds of the Twilight Lake, she is certain she will die.
After all, the Merfolk, the Selkies, the Kelpies, and the Nymphs are her enemies.
It doesn’t matter that the four Fae males who have captured her look like they were crafted by Belisama.
Maeve can’t let her guard down for a moment.
But her mother’s prophecy wears heavy on Maeve’s mind.
“When the five creeds meet over the divide of war, only then will the lake know peace.”
Each of the males is more infuriating than the last.
Can they put aside their differences long enough to end the war under the waves,
or will Fate have other ideas?