North Coast
Hi chatbug. I would head into Sosua and check with Mark at the North Coast Dive Shop, right on the main street in Sosua (Pedro Clisante), it is a green building.
They offer tours, gear, and sound advice if you are heading out on your own. You can actually snorkel off of Sosua beach, which is where many of the catamaran tours will take you from Playa Dorada anyways! You can buy tours at your hotel also, but I think you will pay more there.
Good luck.
marc
