I have never snorkelled there myself but people who have tell me it is very nice. I only know the north end myself. This is one of the most popular snoreling spots on the island. Approach is by road up the side of the hill, park car at top, walk down MANY, MANY steps to the beach. Worth the effort.
Site is in front of Goat Island.
Several operators offer glass boat boat trips out to the reef and most of them combine a tour of the bird sanctuary on Little Tobago Island which is also very good.