you may want to check this out posted by Steve ''My favourite snorkeling place is at Puerto Morelos: Snorkel Tour, Cancun Mexico | Explore Cancun's Secret Reef''
Boris will take you there. We dove it the other day. After about Ten minutes you are bored to be honest. We ended up just exploring around the area and did manage to see a few rays. We are glad we did it, but wouldn't do it again. Ian