The Trump administration on Wednesday denied a key permit for a massive gold and copper mine in Alaska, striking a devastating blow to a project opposed by an unlikely coalition that includes the president’s son and other prominent Republicans, as well as conservationists, commercial fishermen and Alaska Natives.

In a statement, U.S. Army Corps of Engineers Alaska Commander Col. Damon Delarosa said that a plan to deal with waste from the Pebble Mine “does not comply with Clean Water Act guidelines,” and that “the proposed project is contrary to the public interest.”

While the Trump administration has pressed ahead to weaken environmental protections and expand energy development before the president’s term ends in January, the decision to torpedo the long-disputed mine represents a major win for environmentalists, fishing enthusiasts and tribal rights.

“Today’s decision speaks volumes about how bad this project is, how uniquely unacceptable it is,” Joel Reynolds, a senior attorney for the Natural Resources Defense Council, which has fought the mine for years, said in an interview. “We’ve had to kill this project more than once, and we’re going to continue killing for as long as it takes to protect Bristol Bay.”

Trump officials had allowed the Pebble Limited Partnership, a subsidiary of a Canadian firm, to apply for a permit even though the Obama administration had concluded in 2014 that the firm could not seek federal approval because the project could have “significant” and potentially “catastrophic” impacts on the world’s largest sockeye salmon fishery. As recently as July, the Corps concluded that the mine would have “no measurable effect” on area fish populations.

State and federal agencies warned that the project would permanently damage the region, destroying more than 2,800 acres of wetlands, 130 miles of streams and more than 130 acres of open water within Alaska’s Koktuli River watershed. The proposed site lies at the river’s headwaters.

An unlikely coalition of opponents formed when President Trump’s eldest son, Donald Trump Jr., Fox News host Tucker Carlson and Vice President Pence’s former chief of staff, Nick Ayers — who all have enjoyed fishing or hunting around Bristol Bay — joined with traditional environmental groups and the region’s tribes in opposition to the project.

Opponents received a major boost in September when the Environmental Investigation Agency (EIA) released recordings of secretly taped Zoom calls in which the project’s top executives boasted of their influence inside the White House and to Alaska lawmakers to win a federal permit. Alaska’s two GOP senators, Lisa Murkowski and Dan Sullivan, issued statements saying they opposed the plan and within days Pebble’s chief executive, Tom Collier, resigned.

Both senators praised the administration’s decision.

“Today, the Army Corps has made the correct decision, based on an extensive record and the law, that the project cannot and should not be permitted,” Sullivan said. He added that he supports mining in Alaska, but given the project’s potential impact on the state’s fisheries and subsistence hunting, “Pebble had to meet a high bar so that we do not trade one resource for another.”

The Pebble Partnership’s new chief executive, John Shively, called the rejection politically driven and said the firm would consider other options going forward, including an appeal of the decision.

“We are obviously dismayed by today’s news,” Shively said in a statement, adding that the federal government this summer had allowed the project to move forward. “One of the real tragedies of this decision is the loss of economic opportunities for people living in the area.”

He added that the firm had worked closely with the Corps to address environmental concerns.

“All of these efforts led to a comprehensive, positive [environmental impact statement] for the project that clearly stated it could be developed responsibly,” Shively said. “It is very disconcerting to see political influence in this process at the eleventh hour.”

Pebble issued a plan to the Corps this fall outlining how it would compensate for any damage inflicted by the project, which would span more than 13 miles and require the construction of a 270-megawatt power plant, natural-gas pipeline, 82-mile double-lane road, elaborate storage facilities and the dredging of a port at Iliamna Bay.

While the company applied for 20-year permit, Northern Dynasty Minerals chief executive Ronald Thiessen said in secretly recorded conversations that he expected the operation could extract valuable minerals for decades longer than that.

Video recordings show Northern Dynasty Minerals CEO Ronald Thiessen saying U.S. political leaders were not a barrier for controversial mine. (Environmental Investigation Agency)

President-elect Joe Biden has already said he would not allow the mine to be built.

“It is no place for a mine,” Biden said in a statement in August. “The Obama-Biden Administration reached that conclusion when we ran a rigorous, science-based process in 2014, and it is still true today.”

Wednesday’s decision does not necessarily end the years-long fight over the fate of the mine. The firm behind the Pebble Mine could challenge the decision in court or file an amended application seeking federal permits.

At the same time, opponents are hoping that under Biden, the Environmental Protection Agency will use its long-standing authority under the Clean Water Act to preemptively halt projects that the agency thinks will pollute nearby waterways.

Groups that fought the mine expressed confidence Wednesday that it might finally be on its last legs as a consequential transition takes place in Washington. “This project had four years to get an approval in the most favorable political environment imaginable — that is, under the Trump administration,” Reynolds said.

Trout Unlimited President Chris Wood, whose anglers’ group has campaigned against the project, said a decision to deny it a permit is “a victory for common sense. Bristol Bay is the wrong place for industrial-scale mining, and we look forward to working with the state and other partners to protect Bristol Bay and its world-class fisheries permanently.”

Bristol Bay Native Corporation President Jason Metrokin, also its chief executive, said his group and others will keep working “to ensure that wild salmon continue to thrive in Bristol Bay waters, bringing with them the immense cultural, subsistence and economic benefits that we all have enjoyed for so long.”

Adam Kolton, executive director of the Alaska Wilderness League, was among those giving thanks for the decision on the eve of Thanksgiving. Most of all, he was grateful that such a diverse group of opponents had raised their voices, over and over again.

“The credit for this victory belongs not to any politician but to Alaskans and Bristol Bay’s Indigenous peoples, as well as to hunters, anglers and wildlife enthusiasts from all across the country who spoke out in opposition to this dangerous and ill-conceived project,” he said in a statement. “We can be thankful that their voices were heard, that science counted and that people prevailed over short-term profiteering.”