Of Magic and The Sea by Addison Kayne

Kept alive by the thinnest slice of magic. Captive for six centuries in a cavern by the sea, Highlander Lachlan MacGregor drowns with every high tide, only to have his immortal blood revive him day after day.

The only thing that keeps Lachlan from slipping into madness is the one human emotion to which he still clings. Hope.
Unwelcome psychic visions have plagued Brenna Sinclair her entire life. This time, Brenna doesn’t just see a man in desperate straits. This time, she’s coughing up salt water from her lungs. This time, the connection is more than psychic.

Aided by ancient mystical relics from a time long ago when dragons ruled the skies, Brenna risks her life and embarks on a journey to rescue a drowning man.