Snorkeling Excursions in Cozamel?

What do you recommend for a one day snorkeling excursion? We will be on Carnival.

I would go over to Trip Advisor and read reports regarding best places to snorkel in Cozumel. Also, go to ports of call here, and click on Caribbean. You can scroll down to Cozumel. There are places that you can snorkel right from the shore over there. I do know that the area took a big hit when the hurricane came through years ago. Some areas may not have come back.