I think we were luck to get an exceptionally low tide one afternoon.
Earlier in the morning I had snorkeled right over this area of the reef!
The "bird's eye view" from our glass bottomed boat was spectacular!
On the horizon, you may see some waves breaking... that is the edge of the reef and the end of the continental shelf. Using numbers, that means that we went from about 30 to 50 ft deep water to a few thousand feet deep.