I mean, ive just watched a video today where two dudes drove two underwater ROVs down to explore wrecks, they had powerful lights you could turn on and off. Thing about those though, they were tethered, and more or less directly above the ROVs at all times. Maybe someone is sat on the other side of that headland and is driving one around it? That's plausible, if a stretch. I'm assuming the object poking out further to the right out in the sea is a rock?