back at the pontoon , plunge beneath the surface , snorkeling or scuba diving or in a semisubmersible vessel with picture windows , and enter an underwater world unlike any other : living coral in brilliant orange and yellow and red and blue ; jagged cliffs and rocky boulders , one amazing formation after another ; blue-spotted trout and green-and-red parrotfish and their kinfolk swimming past by the thousands , unperturbed by human intruders .