The Marietas Islands are an excellent choice if you don't mind the long boat ride - lots of fish, coral, and things to see.
Please note that the water temperature at Marietas is a few degrees cooler than the sites closer to shore.
For safety reasons, expecting mothers and people with back, heart or neck problems are not permitted. People older than 65 years old can't do this activity. For snorkeling, guests must know how to swim and should have a general level of comfort putting their face in the water.