Part of our weekly "In Focus" series—stepping back, looking closer.

Mostly roadless and undeveloped, the Bristol Bay watershed doesn't look like a battlefield, yet it has become the Gettysburg of natural resource conflict in Alaska.

Located some 250 miles (400 kilometers) southwest of Anchorage, the 40,000-square-mile (104,000-square-kilometer) region is home to the largest population of wild salmon in the world. Every summer, 30 to 40 million adult sockeye salmon return to the bay, then swim upstream to complete an ancient cycle of renewal. And that's where two vastly different interests have clashed, because located in the upper reaches of the spawning grounds, a few miles north of Iliamna Lake (map), is a world-class ore deposit containing about 80 billion pounds (36 billion kilograms) of copper and 110 million ounces (3 million kilograms) of gold.

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On one side of the conflict are two companies—Northern Dynasty Minerals, of British Columbia, and Anglo American, an international behemoth headquartered in London. Called the Pebble Partnership, after the name of the mine they have proposed, Northern Dynasty and Anglo insist that a large-scale industrial enterprise—including a pit mine up to 2 miles (3.2 kilometers) wide and 1,700 feet (520 meters) deep, a comparable underground operation, a mill to crush and separate metals, and tailings ponds that likely will dwarf the mines—would pose no serious threat to habitat and wildlife. (Video: Pebble Mine would pit gold against salmon.)

Opposing the Pebble Partnership is an uncommonly savvy patchwork of native groups, commercial fishermen, village councils, local residents, outfitters, conservationists, and others united in the conviction that the environmental risks, especially for salmon, greatly outweigh the economic benefits. (Read about an earlier chapter in the Pebble Mine story in the December 2010 issue of National Geographic magazine: "Alaska's Choice: Salmon or Gold.")

After numerous skirmishes involving state petitions and legislative initiatives, lawsuits and public opinion campaigns, the battle may have reached the final stage, or at least a turning point in how Alaskans resolve disagreements over the exploitation of natural resources, long the backbone of the state economy.

Enter the Feds

Back in May, the U.S. Environmental Protection Agency released a draft assessment of the potential consequences of a Pebble Mine-like development in the Bristol Bay watershed. Even under the best conditions, the agency concluded, 55 to 87 miles (90 to 140 kilometers) of pristine streams would be destroyed, along with up to 2,500 acres (1,000 hectares) of wetlands. Most worrisome, the EPA noted, is the risk of a catastrophic failure of one of the mine's tailings ponds, where residue from the mill would be held. If a pond were to fail, it would release acidic water and heavy metals into spawning grounds, causing grave, irreversible damage.

State officials and the Pebble Partnership immediately dismissed the findings and denounced the EPA. A period of public comment followed. Then, to further ensure the integrity of the process, the EPA convened a 12-member peer review panel of independent scientists to evaluate the draft study. On November 9 the panel released its report, largely confirming the reliability of EPA's original assessment. "Given the extremely long-term nature of the project," one reviewer wrote, "the risks seem, if anything, understated."

Mining always entails risk, of course, and the independent report is "not a showstopper," admitted Rick Halford, a former state legislative leader and lifelong pro-development Republican who, to the surprise of many and dismay of some, has teamed up with the cold-water fishery conservation group Trout Unlimited and others to stop the mine. "But it could make it very difficult for the partnership to go ahead with its plan."

Preventive Measures

For years, the Pebble Partnership's standard response to such criticism has been to say no plan exists, meaning the partnership hasn't yet filed an official mine design with the state, which is true. Therefore, as Pebble CEO John Shively argued in a press release last May, the EPA draft assessment is "rushed," "inadequate," and, most of all, premature.

But opponents like Halford and others familiar with the regulatory process in Alaska worry that if the project gets that far, approval will be all but certain. And besides, they point out, back when Northern Dynasty, a small, exploratory company, was courting transnational mining conglomerates like Anglo American and Rio Tinto, it did in fact release a preliminary plan, touting the size and monetary value of the deposit.

Most independent experts who have examined the preliminary plan believe it accurately reflects the nature of the deposit and its remote location. The exact size of the pit mine, underground excavation, and tailings ponds may be uncertain, but the overall scale isn't hard to predict. If the operation isn't large enough, it won't be profitable. And no one questions the need for an 86-mile-long (138-kilometer-long) corridor—a haul road and pipeline that would cross dozens of spawning streams—connecting Pebble to Cook Inlet, nor that the port would have to be turned into a deepwater facility.

Whether power would also be brought in through the corridor or produced on site is uncertain, but at peak operation, the mine could require up to 300 megawatts, enough to supply a midsize city. All of this would take place in a region that today is mostly wilderness.

Another indisputable feature of the mine would be the need for monitoring and maintenance after it ceases operating. Not for 10 years, or 50, or 100, but forever. Every tailings pond in the world that's been examined closely has shown signs of leakage, which tends to accelerate over time. Many tailings dams, which hold the ponds in place, have collapsed. To make matters worse, Pebble would be located near a fault. The exact location of the seismic zone is uncertain. Some USGS maps suggest a distance of 5 miles (8 kilometers), whereas the Pebble Partnership is likely to design its tailings impoundments based on the assumption the seismic zone is 18 miles (29 kilometers) away.

Either way, it will be a considerable gamble. Trusting a corporation, whose only enduring loyalty is to its officers and shareholders, to maintain in perpetuity immense man-made structures in sensitive environmental locations may seem like folly, but that is exactly the pledge the Pebble Partnership will make when it eventually submits a plan—because that is now what the law requires.

A Bold Move

In 2010, fearing that state officials don't comprehend or care enough about the hazards Pebble poses, nine Bristol Bay tribal governments petitioned the EPA to intervene. Citing a provision of the U.S. Clean Water Act, which governs dumping waste in streams, the Native American groups implored the agency to block the mine. The agency decided that, before it could take any action, it needed to know more. So it set out to examine the possible effects of an industrial mining endeavor in the watershed.

Bypassing the state was a bold move. "For Alaskans to go to a federal agency for help is unheard of," Halford explained. Governor Sean Parnell was furious. His attorney general sent letters to the EPA accusing it of overreach and threatening legal action. Equally indignant, and fearing it was in danger of losing the battle, the Pebble Partnership went to great lengths to stir up states'-rights sentiment.

That might have worked in the past, or regarding another mine in a different location, but something had shifted in the Alaskan soul. Of the 230,000 public comments the EPA received regarding the draft assessment, 98 percent opposed the mine. Even the conservative Anchorage Daily News endorsed the federal assessment process, asserting in a blunt May 3, 2012, editorial that the EPA was doing what it "should be doing," while decrying the passivity of the Parnell administration.

The EPA hasn't indicated when it will release the final assessment, nor whether it will do anything beyond making recommendations, but it has the authority to impose restrictions that would effectively prohibit any large-scale industrial operation, including Pebble. Convinced that they can't trust the state government to look out for their interests, those opposed to the mine believe that protecting the planet's largest and most robust wild salmon fishery—and, by extension, all that makes the Bristol Bay watershed distinctive—now depends in large part on convincing the rest of the country that a treasure of singular national importance is imperiled.