You should probably give serious consideration to getting your own mask and snorkel.

However, if you don't end up taking care of that before you leave home, don't worry about it. As long as you are taking your course with one of the reputable operators you should be just fine.

That said, aside from all the other reasons, despite the snorkeling off of the beach not being so great in SP, it is still nice to be able to go out on the end of a dock and paddle around. If you have your own mask and snorkel, you can still see all kind so things.

A fish and a bird can fall in love, but where will they build their nest?