The Environmental Protection Agency announced Friday that it will examine whether to block a massive gold and copper mine proposed in Alaska — marking a major win for native Alaskan tribes, commercial fishing operations and environmentalists who have been seeking to kill the project.

A Canadian-based firm, Northern Dynasty Minerals, is trying to start construction on the Pebble Mine project, which it predicts will create 1,000 direct jobs and generate up to $180 million in state revenue. It would also result in dumping waste into the surrounding Bristol Bay watershed.

The EPA is invoking its authority under the Clean Water Act to determine whether it should permanently bar the U.S. Army Corps of Engineers from issuing a discharge permit for the mine. Bristol Bay is home to a critical fishery that supports nearly half of the world’s sockeye salmon.

“Extensive scientific study has given us ample reason to believe that the Pebble Mine would likely have significant and irreversible negative impacts on the Bristol Bay watershed and its abundant salmon fisheries,” EPA Administrator Gina McCarthy said in a statement. “This process is not something the agency does very often, but Bristol Bay is an extraordinary and unique resource.”

Although the announcement does not mean the Obama administration has made a final decision, the move will delay construction for months and make it harder for the controversial project to move ahead.

Tom Collier, chief executive of the Pebble Limited Partnership, issued a statement calling the move “a major overreach onto an asset of the state of Alaska.”

“The steps taken by the EPA to date have gone well outside of its normal practice, have been biased throughout, and have been unduly influenced by environmental advocacy organizations,” he said.

Sen. Lisa Murkowski (R-Alaska) accused the EPA of issuing a “preemptive veto” that could set a dangerous precedent.

But Michael Conathan, who directs ocean policy at the liberal think tank Center for American Progress, said it made sense for the agency to weigh in before the company “invested additional resources.”

Several Democratic senators, including Maria Cantwell (Wash.) and Mark Begich (Alaska), had pressed the administration to halt the project on the grounds it could affect fishing jobs across the Pacific Northwest. “Today, the administration is saying that potential gold mining is not more important than a $1.5 billion sockeye fishing industry,” Cantwell said.

White House press secretary Jay Carney characterized the move as part of President Obama’s broader effort to protect public lands and waters.

“The White House strongly supports that decision by the EPA,” Carney told reporters Friday. “The step is consistent with the president’s commitment in the State of the Union to protect pristine American places for future generations.”

Although it has not generated the same national attention as high-profile projects such as the Keystone XL pipeline, Pebble Mine has become a major issue for conservation activists.

“It’s difficult to imagine a more significant conservation achievement than protecting Bristol Bay,” said Chris Wood, president of the advocacy group Trout Unlimited.

The EPA issued a scientific assessment last month that concluded that up to 94 miles “of salmon-supporting streams and 1,300 to 5,350 acres of wetlands, ponds, and lakes” would be eliminated by the footprint of a mining pit, depending on its size. Several native Alaskan tribes have done subsistence fishing there for centuries.

In starting the months-long process, the EPA sent a letter to the Army Corps, the state of Alaska and the mine’s sponsor to ask why they believe the operation would not damage the pristine watershed. The recipients will have 15 days to respond, though the agency can extend that deadline.

After that, the EPA’s regional administrator in the Pacific Northwest will issue a “proposed determination” that will lay out whether the company can discharge waste into the area and, if so, where and how much. The public will have an opportunity to comment on the proposal, after which point the regional administrator will send a recommendation to EPA headquarters.

Jason Metrokin, president of the Bristol Bay Native Corporation, welcomed the decision but said, “There’s no reason for anyone to declare victory” yet.