Grenada is an amazing destination, and has some OK snorkeling, but snorkeling is not its strong suit. Whenever you have a lush island with rivers and substantial rainfall, the run-off into the sea tends to cause cloudiness in the water -- hence visibility is not as great as it would be on some of the more desert-y islands. As well, some of the coral was damaged by the heavy seas caused by Hurricane Lenny a few years ago. That said, Grenada is a good jumping-off spot for a day-trip or two to great snorkeling, such as the Tobago Cays in the Grenadines, or Sandy Island off of Carriacou.

We stayed at Spice Island in Grenada and spent a few days snorkeling. A guide "Captain Peter" who hangs on the SII beach took us on his boat to a nearby inlet to snorkel and we thought it was very good. His wife cooked a native lunch for us under a palm tree and the price included all drinks too. I forget what we paid - but it was reasonable.

i went to grenada in april, and agree about the cloudy water. however, we took a day trip to sandy island off of carriacou and the snorkeling was very good.

are you stuck on grenada? for great snorkeling you might want to try st. john... or cayman islands...

HKR,
There are many Caribbean islands with notably good snorkeling - but Grenada is not one of those usually cited.
Try St. John, Cozumel, Virgin Gorda, Caymans, St. Lucia, Out Islands of the Bahamas (though not in the Caribbean), Turks and Caicos.