Whew...could you narrow it down a bit?
The barrier reef is ~130 miles long, if you take the rough linear distance of the 3 atolls thats another ~130 miles of reef (not including the thousands of corals heads and patch reefs
inside the atolls), and to that all the inumerable reefs
heads inside main barrier reef...thats a lotta reef, with thousands of good snorkel/dive spots.
Are there specific areas in Belize
that interest you?