My comments above were fyi mainly for @Anilo182 in case they weren’t aware.
Snorkeling is not particularly good but it depends how experienced you are and what you are expecting.
If you don’t need the facilities of a large resort or AI and just want to snorkel and a snack I would check out websites and reviews for Sky Reef, Money Bar, El Cid, Del Mar, Tikila Bar, La Monina or Buccanos. (South to north)
Prices for taxis to all these places will be on a board at the port. El Cid, Del Mar and Tikila/ Sunset Bar are within reasonable walking distance of Puerto Maya if you are active. Use Google maps for interactive walk. La Monina and Buccanos are north so slightly different to Chankanaab area. To get the best experience at any of these locations it is probably best to ask the locals regarding currents and areas to aim for. Between Tikila and Sunset are underwater statues. Offshore at El Cid is an underwater plane wreck I haven’t seen it, only read about it, and you would need a day pass from lobby.