Hi there,
There is no shore diving on north Ambergris Caye, however, the resort i work for (Tranquility Bay Resort) is the last resort and the closest to the reef. You can snorkel to it or kayak and the diving is just the other side of the reef, so a 2 minute boat ride. The snorkeling here is amazing and very shallow, deepest point is about 5/6 feet. Also it is very safe as being the last resort we do not have much boat traffic at all.
The diving is great too, as I said a 2 minute boat ride so you can do your surface interval back at the resort. Plus as so few people come up here most sites are relatively unexplored. Whenever I have free time I am either diving or snorkeling!
Either way the diving in Ambergris Caye is great and there are trips to the offshore atolls as well.
I hope this helps!
Megan