What’s the greatest threat to Alaska’s pristine wilderness?

Drilling in the Arctic National Wildlife Refuge is up there, as is climate change. But if you ask people who live in the state, many will tell you that Pebble Mine—a proposed open-pit copper and gold mine that would be as much as two miles long, a mile and a half wide, and 1,700 feet deep—is their biggest environmental concern. It’s also one that the Obama administration Environmental Protection Agency could actually stop.

If built, Pebble Mine would be the largest mine of its type in North America. It would sit at the headwaters of the Nushagak and Kvichak rivers, which feed into the Bristol Bay, producing as much as 11 billion tons of toxic mine waste over a span of decades. The waste would be stored in earthen dams near the site. In its latest report on the potential project, the EPA found that the footprint of the mine could destroy as much as 90 miles of streams and 4,800 acres of wetlands—and that’s just from habitat destruction. It doesn’t include the impacts of leakage from tailing ponds or other accidents. (Mother Jones covered the potential impact of the massive project back in 2006.)

After a decade of talking about building Pebble, the company behind the plan still has yet to begin applying for permits. The Pebble Partnership—formed by two mining giants, Northern Dynasty Minerals and Anglo American—says it is still conducting geologic and environmental studies. Critics of the project say they’re waiting for an administration that might be more likely to approve it. Three years ago, this still-uncertain fate prompted a group of six Alaska native tribes to ask the EPA to step in and assert “veto authority” over the mine under a provision of the Clean Water Act known as 404(c). The EPA can invoke this provision if it finds that waste disposal from a project would have “unacceptable adverse impact” on waterways, fisheries, or wildlife. Invoking 404(c) is pretty rare, however; the EPA has only done so 13 times since 1972.

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