According to Grenada Explorer, the very best places for a beach snorkel in Grenada are at the beaches near the Aquarium:

Magazine Beach

If you are looking for good snorkeling sites close to the shore, then the best place to visit would be the beaches near to the Aquarium Restaurant or Rex Grenadian Hotel.

To get there, you will need to take the main road past the airport terminal until you see the sign for the restaurant on your right.
This beach offers sheltered areas, gorgeous white sand and snorkeling along its southern end.

The Aquarium Restaurant & Beach Club is a good place to make the day more enjoyable, and makes a comfortable base for the afternoon. Refreshments are available on the beach, beach chair rental, hotel & restaurant, shade, small coral reefs and good snorkeling!

FROM: Grenada Beaches