More than a thousand miles of vibrant colors, tropical species, and open sea, it already contains the largest marine park in the world. Now a bold new plan could increase protected areas sevenfold, but not everyone approves. Above and below the water, Mike Di Paola confronts the caretakers of the Great Barrier Reef

The dive site is known as The Bommie, but it is in fact many bommies, or coral outcrops, lined up here in huge columns and submerged in forty-five feet of crystal clear water. In a gentle drift dive like this, the ocean's current pushes me along and I don't need to kick my fins much, so I can almost simulate flight. But being the way I am, I do at least as much air supply-monitoring as fauna-gawking. A pity. According to the excited accounts of others on the dive boat, I missed seeing the green sea turtles, a couple of laggards in the mass migration that peaks in this part of the Great Barrier Reef in October; a spotted wobbegong shark that blended in with the scenery on the seafloor; and a moray eel. Maybe so, but disappointment never entered my mind, because I did see an endless parade of fish, including an impressive school of chevron barracudas, passing by with unnerving insouciance.

And, as remarkable as the motile creatures are, it is the ones that don't pass by—the corals—that are so visually arresting. I drift through the panoply of colors and shapes, between hard corals of boulder, brain, mushroom, and honeycomb, among softer varieties such as broccoli, spaghetti, and elephant ear.

Australians cannot be accused of taking all this beauty, this fecundity, for granted—especially now that the government is proposing to expand the most heavily protected areas in the Great Barrier Reef Marine Park. It's already the largest marine preserve in the world: some 138,000 square miles, a region as big as Finland stretching north from the Tropic of Capricorn, with more than 2,900 coral reefs, three hundred coral cays, and another six hundred continental islands. But currently, less than five percent is actually part of the Great Barrier Reef National Park—patches called Green Zones, where fishing and other acquisitional activities are prohibited. Under the proposal announced last summer, the national park will expand to include thirty-two percent of the reef.

This is good news for the coral, fish, and other fauna that inhabit the reef, as well as for the divers, snorkelers, yachtsmen, and other visitors, because Green Zones will continue to allow access on a look-but-don't-take basis.

I arrived at Heron Island by helicopter, a ride that delivered me from industrialized Gladstone to the grandeur of the reef on its horizon. The aerial retreat from the factory town is revealing—power plant generators push white haze into the sky above dozens of coal-filled railcars and an aluminum factory. The bay, repository for the effluences of three rivers, is a silty brownish red—which quickly turns brilliant aquamarine as you soar out over the Coral Sea.

Though delirious with jet lag from crossing fifteen time zones, I jump in on a bird-watching tour of Heron Island. I'm no birder, but I'm not above any practice that will supply me with arcane trivia I can one day use to wax pedantic. And anyway, I need something to keep my corpse upright until it's really time for bed.