The Pacific-side of Costa Rica is not known for great snorkeling, as in the Caribbean. However, sometimes conditions are right and snorkelers are treated to an abundance of fish, like when the waves are calm and there hasn't been any rain in awhile. For the best snorkeling, I combine it with a Sunset Cruise on a catamaran, and let the Capitan use his judgement as to where to find the best snorkeling; it's part of his job. The cruises have food, snorkeling gear, in-water guides, etc.