"Some of the best diving I've ever done is snorkeling in Cancun..." You're on the surface, generally with a life vest, don't have to worry about running out of

"Some of the best diving I've ever done is snorkeling in Cancun..." You're on the surface, generally with a life vest, don't have to worry about running out of air, generally the guides inter-communicate and take you to hot spots of fishes or turtles or whatever... tropical warm water. Biggest difference is access to air rather than having to be "self-sufficient".