I don't know why you wouldn't enjoy the ease of diving off Ambergris Caye. The dive sites are only 5-20 minutes offshore. The best snorkeling is also done off a boat. There are a couple of places at the end of some docks, most notably Ramon's, that you can find some enjoyable snorkelling but other than that, from the resort(s) . . .nada.

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