Yes, we booked the excursion in Belize through Carnival. It was actually nice to have a guide while snorkeling. They had 2 groups, one that went off the beach, (which I did) and the other off the boat on the other side of the small island. Seems most just stayed on the boat and I jumped off and ended up with a group of 5, while the other group had 25, so it was really nice. The guide would go down with your camera and also point things out along the way, things I would have missed myself.