SEATTLE — The largest open-pit mine in North America, proposed for Alaska’s wild and remote Bristol Bay region, would have a devastating effect on the world’s biggest sockeye salmon fishery and the Alaska Natives and fishermen who depend on it, according to a federal report released this week.

After completing three years of scientific study, conducting eight hearings and sifting through more than a million public comments, the U.S. Environmental Protection Agency concluded Wednesday that the proposed Pebble Mine could destroy up to 94 miles of streams where salmon spawn and migrate and up to 5,350 acres of wetlands, ponds and lakes.

Even using the most modern mining technology, the study said, polluted water from the mine site could affect fish in up to 51 miles of streams.

Piles of mining waste “higher than the Washington Monument are likely to be in place for hundreds and thousands of years, long beyond the mine itself,” said Jeff Frithsen, senior scientist with the EPA’s research and development office.

The failure of these so-called tailings dams, which would be used to hold back toxic waste from the mining of copper, gold and molybdenum, “would have major catastrophic impacts on fish and fish habitats impacting large areas for decades,” Frithsen told reporters.

In 2010, tribes and others in Bristol Bay, a region about the size of Ohio with more brown bears than people, asked the EPA to protect the watershed. But the agency said it first needed to study the potential effects of the proposed mine.

Bristol Bay is home to what a University of Alaska Anchorage study described as “the world’s most valuable wild salmon fishery,” which “typically supplies almost half of the world’s wild sockeye salmon.” The multiplier effect of harvesting, processing and retailing Bristol Bay salmon, the report said, was worth $1.5 billion across the United States.

Under the Clean Water Act, federal environmental officials have the authority to prohibit, limit or restrict the disposal, discharge or long-term storage of mining waste into waters within the United States.

But Dennis McLerran, who heads the EPA office that oversees the Pacific Northwest, emphasized Wednesday in a call with reporters that the study is just that — a peer-reviewed analysis that will inform his agency’s future actions.

“We have not made any decisions with respect to regulatory actions,” McLerran said. “That comes next, and a response to the tribes is what we’re most concerned about developing next. … We have no set timeline on that.”

Alaska Gov. Sean Parnell, a Republican, questions the EPA’s intentions. “This report is little more than a pretext for an EPA veto of the state’s permitting process,” he said, adding that every permit application “deserves scientific and public scrutiny based on facts, not hypotheticals.”

John Shively, chief executive of Pebble Limited Partnership, which is developing the controversial mine, called the EPA’s study a purely “political document” done in haste — one that ignores the modern engineering and mitigation measures the group would need to include to get permits.

“About 90 percent of our tailings are not toxic,” Shively said in an interview. “They’re just dirt. There isn’t a way even under the worst possible circumstance that we could destroy that fishery. It’s just not possible.”

But environmental and Alaska Native groups lauded the study’s conclusions and called on the EPA to act immediately.

“It’s the worst possible place to do this type of mining — the headwaters of the Bristol Bay fishery next to a national park,” said Melissa Blair, Alaska program manager for the National Parks Conservation Association. “We can look at this technically and say the risks are too great and (mining) shouldn’t happen. It’s not worth trading the fishery.”

The EPA’s assessment notes that “up to 15 more mines could be developed if Pebble is allowed,” Blair said. “Pebble would be the tip of the iceberg. Next to the national park, an industrial mining district could be developed that’s much larger than just Pebble.”

Shoren Brown, executive director of Bristol Bay United, called the report “a smoking gun for the Pebble Mine.” The group is a coalition of sport and commercial fishing interests and Alaska Native corporations.

“The science that we’ve been waiting for, for three years, is now absolutely in,” Brown said. “The only question is what this agency and administration are going to do now that we have thousands of pages of documentation that says this mine will cause huge impacts to the world’s greatest wild salmon fishery.”

Jason Metrokin, chief executive of the Bristol Bay Native Corp., becomes well nigh poetic when he talks about the region. “God’s country” is how he describes it — home to moose and caribou, mountains and one of the nation’s largest lakes.

Between 40 million and 60 million salmon return to the region every year, he said. Native culture and well-being depend on them, and so does the commercial fishing industry.

“Large-scale hard-rock mining will have adverse impacts,” Metrokin said. “Can there be a future mine in the Bristol Bay region that doesn’t have adverse impacts? We don’t know. All we know is that there is one project proposed.”

Photo via Wikimedia