Can thoroughly recommend Shinaria as a snorkelling venue, as did this a couple of days. Lefgoiya is also worth a go (the one before Shinaria and after Damnoni).
Also well worth a snork is the beach by Taverna Gallini - Souda - go right out by the headland, there are some really good hidden coves round there - but watch out there is a big eel in one of them. The water is crystal clear and easy snorkelling but do invest in a pair of fins, I bought a new pair this year from the Forum Supermarket, only 17.50 Euros - bargain.
Enjoy, because we did.............
Pritch