I don't know about Caye Caulker but....
There is good snorkeling on Ambergris Caye at the Tranquility Bay Resort. You can snorkel right from their beach out to the reef and there is little to no boat traffic in that area. I believe it is the only resort that actually has decent snorkeling on site.
Aug 27, 2011 Rating
Snorkeling Cay Caulker by: Galen & Nicole
Cay Caulker is more laid back and a bit less touristed than Ambergris Cay. But I do not believe there is any good snorkeling from shore on Cay Caulker, so you will need to take boat trips out to the reef. I know that they run trips up to Hol Chan and Shark Ray Alley, the same as would happen from Ambergris. But you probably will also be able to snorkel some of the closer reef cuts near Cay Caulker, at North Pass and at South Pass. The barrier reef is about a bit over a mile from Cay Caulker. You may just want to call ahead of time and confirm what trips are available, because it may be more limited than at Ambergris. Have fun!
Aug 29, 2011 Rating
Caye Caulker Snorkeling by: Anonymous
Caye Caulker has the same trips available with many different companies as Ambergris does. There is some great snorkeling in Caye Caulker at the split! Caye Caulker is just a much more chill, laid back island than Ambergris!