There is a beautiful shallow water reef near the west end.
Anyone who PM's me I'll tell you where it's at, easily accessible and relatively unknown.

I have swam and snorkeled a lot on the west end.
I found that if you go around the point from Xtabi toward Ricks (in front of 3 Dives and beyond) it's good snorkeling and you'll be able to entertain yourself for a couple hours.
Some people say don't feed the reef fish, let your conscience be your guide.
That said, use bagels instead of bread, bagels hang together better.