My wife and I are headed back to ERC in December (for the 3rd time).
On our previous trip in Oct/10 there was a tour boat located between ERC and the resort next door (Dreams). They charged $25/person to head out to the reef for a couple hours of snorkeling with a tour guide (at two spots), as long as they had 4 people in total. It was quite convenient as we didn't need to find our way into Puerto Morelos for essentially the same price/experience.
The boat/tour operator was there throughout the 10 days of our trip, and we went out twice in a small group of four people.
Does anyone know if this opportunity still exists?