Last year when we were there we snorkeled in the first spot GradUT mentioned. It was a bit annoying getting there because the beach directly in front of the snorkeling area is private, reserved for one of the private cabanas. We had to walk from the public beach area in the water over to the snorkeling area. The snorkeling was just ok. We had our own gear. We will be back to HMC this December and probably won't bother snorkeling. We will be diving in Curacao and Aruba though.