The Coco Islands are famous for two things: the unique weathered rocks and the ideal for snorkeling reef, where you can see neon coral fish, the size of a centimeter, reef shark, a metre and a half long. Coco Islands has been a marine park since 1996. You can well see the reef between the islands in the photo below. This is where you will find great snorkeling.
All lovers of snorkeling strongly recommend swimming in clothes, because for half an hour you can get completely burned.