Pescador Island is the classic boat trip from Moalboal. The island itself is small and not the point; the draw is the surrounding reef, with walls, coral, and fish life that make it one of Cebu's better-known dive sites.
Snorkellers can enjoy the shallower edges in calm weather, but divers get the fullest version. Conditions and currents matter, so choose an operator that is clear about where it is safe to enter and what the sea is doing that day.