In Mexico we have a season where you can do snorkeling with the whalesharks. That is from June to August. They don’t move fast and they are friendly. By far a great experience !!! I try to go every year.
You can take the trip from Cancun. They are many companies to take the tour. It is an all-day trip. Normally the trip includes round tranportation, lunch and soft drinks. They use fast boats.