was snorkeling the warm, clear waters of the Dry Tortugas off Florida last summer, just as a hard-won deal to turn it into the largest fully protected area of underwater America was being clinched. Shimmering shoals of baitfish, schools of blue-and-yellow striped grunts, and haughty-looking queen angelfish the size of saucepans swam past me. There were brain and rock corals, branching staghorn, and lacy sea fans. I spotted a five-foot nurse shark, and held my breath to hear the big aqua-green, red, and purple parrot fish grazing contentedly on the coral. Above the surface, squadrons of chevron-tailed frigate birds patrolled, searching for flying fish and other easy pickings.

Dry Tortugas is 151 square nautical miles (soon to be 197) in which fishing, drilling, dumping, treasure hunting, and anchor dragging are no longer allowed. Nor is any other activity that threatens the natural wonder of the place, which offers its visitors the genuine National Geo experience. You can come to snorkel, sail, or dive. But take only pictures and leave only bubbles.

If all goes well, Dry Tortugas may be only the first of a string of new underwater wilderness parks. There are projects now afoot to establish fully protected ocean areas in the Gulf of Maine, off Washington State, and elsewhere. But the most promising effort -- and the most contentious battle -- is taking shape in California. The state already has a few small marine reserves, just two-tenths of 1 percent of its coastal waters. Now, a pro-conservation coalition is trying to win enough popular support to create what could one day be the nation's most complete network of underwater wilderness.

Yes, wilderness. "I am glad I shall never be young without wild country to be young in," Aldo Leopold once wrote. "Of what avail are forty freedoms without a blank spot on the map?"

As terrestrial beings, we tend to forget that most of our planet's surface remains a blank spot. We've mapped less than 5 percent of our oceans with the accuracy we've achieved in mapping 100 percent of the moon. We're only now discovering and exploring previously unknown ecosystems, such as deep-ocean coral forests, hydrothermal vent communities, and the craggy slopes of submarine mountains. Yet the oceans contain more than 80 percent of all species and 95 percent of all livable habitat. They represent a second chance to do right by the wilderness that gave birth to us all.

In 1890 the U.S. Census Bureau declared the American frontier closed. But in 1983 Ronald Reagan, in one of his most significant and least noted acts, created a new frontier. Following international precedent, he established a 200-mile-wide Exclusive Economic Zone stretching out from America's shores, a wild new territory six times the size of the Louisiana Purchase.

For the most part, we've continued to treat this blue frontier much as we treated our original frontier -- as a place to drill for oil, dump our wastes, and slaughter wildlife. In 2000, however, a National Academy of Sciences report called for wilderness protection for a fifth of America's coastal waters, in order to sustain dwindling fisheries and wildlife populations. Bill Clinton then issued an executive order establishing the framework for a national system of protected marine areas. He also created the Northwestern Hawaiian Islands Ecosystem Reserve, a vast oceanic extension of the island chain.

But in the mangrove tangle of overlapping jurisdictions and special interests that governs offshore management, protecting ocean wilderness may prove even more challenging than protecting terrestrial wilderness.

ou have to balance the interests of the environmentalists with our right to make a living," says Bob Fletcher, the tall, trim, gray-eyed president of the Sportfishing Association of California. We're at a sport fishing landing on San Diego Bay, and the docks behind Fletcher are lined with dozens of big party boats emblazoned with names like Top Gun, Prowler, and Conquest.

Recreational ocean fishing is big business in California. In the aggregate, Fletcher and his colleagues make $2.5 billion a year taking their clients out to hunt fish with sonar. The industry has responded to steep declines in California fisheries by redefining trophy fish. In the 1960s, for instance, mackerel was used as bait. Now that many of the big fish are gone, mackerel is on the industry's list of daily catches. The recreational fishing industry doesn't sell fish, however. It sells the "experience" of fishing. And many of its clients lack the long-term perspective to notice the changes.

"I think reserves will decrease rather than increase yields," Fletcher tells me. He argues that closing an area of the ocean to fishing means closing off its contribution to the catch, and he claims that traditional management can restore fisheries. "If we get reserves at the levels environmentalists want," he warns, "you'll devastate opportunities for recreational fisheries and anglers."

What has Fletcher so concerned is the state's Marine Life Protection Act. Originally supported by NRDC, the Orange County Marine Institute, and other conservation and marine education groups, it was celebrated as a major environmental victory when it became law in 1999. The act called for the creation of a large network of fully protected areas along the state's 1,100-mile coastline by June 2002.

That's not going to happen. In July 2001 the Department of Fish and Game released initial maps of the planned reserves. But the maps had been put together with little input from the fishing sector or other stakeholders among the general public -- an act of political bumbling that set off a series of angry public hearings. The deadline was rolled back to December 2003.

Today, California is in the midst of a public comment period in which the state must gather input from stakeholders and use it to redraw the maps. The sport fishing industry is the leading force pushing for minimal reserves. "Let's not alienate everyone," Fletcher says. "Let's start small, move [the reserves] away from the coast, and document them over five to ten years."

It occurs to me that if either side isn't satisfied with the state's final recommendations, they might sue. Wouldn't the result be years of additional delay, I ask Fletcher, with the reserves tied up in court indefinitely?

"I don't see that as such a bad thing," he says, grinning. "I'm not against inaction."