Song of the Sea King by Alessa Thorn

The seas of Faerie and Albion need to be healed in order for magic to flow again, and it’s up to one surly fae king and a lighthouse keeper with a strange gift to get the job done.
Mananan has to fix the oceans between Faerie and the human world to stop them both from dying. With a god killing sword and a willingness to use it, he’s more than up to the task of defeating any monsters their enemies throw at him. The problem is, he needs to find the altars that are sucking the magic from the sea, and he has no idea where to start looking.
Ella’s magical talent for seeing visions whenever she touches something has ensured she lives in seclusion and privacy. That is, right up until a kraken attacks her light house, and she is saved by Mananan. Being indebted to one of the fae is a dangerous business, but Ella has no choice. She has a skill they need to find the altars, and there’s something about her that Mananan can’t resist.