The Biden administration has blocked a controversial proposed gold and copper mine in Alaska in order to protect the world’s largest sockeye salmon fishery. 

The Environmental Protection Agency (EPA) blocked construction for the Pebble Mine, citing its potential impact on Bristol Bay — a southwestern Alaska watershed that’s home to numerous animal species including the salmon. 

The decision, announced on Tuesday, is not a surprise, as the administration had proposed to block the mine last year. But, Tuesday’s action officially prevents its construction. 

EPA Administrator Michael Regan told reporters that the agency had determined that discharges that would come from the proposed mining would have “unacceptable adverse effects” on salmon fishery areas.

“As a source of food and jobs and a means of preserving sacred indigenous customs and practices, Bristol Bay supports the livelihoods of so many,” he added. “This final action demonstrates the Biden-Harris Administration’s commitment to safeguarding our nation’s indispensable natural resources.”

Specifically, the EPA’s action prohibits the certain waters from being used as disposal sites for mine waste and prohibits future proposals to mine the Pebble deposit that would have similar environmental impacts. 

The company behind the mine, the Pebble Limited Partnership, threatened a lawsuit over the EPA’s action.

“Unfortunately, the Biden EPA continues to ignore fair and due process in favor of politics. This preemptive action against Pebble is not supported legally, technically, or environmentally. As such, the next step will likely be to take legal action to fight this injustice,” said CEO John Shively in a written statement . 

He added that the mine would bring “jobs, economic activity, revenue, and infrastructure” and argue that the minerals could be used to further the green energy transition. 

The issue has pitted mining interests against fishing and environmental interests and sentiment surrounding it has not fallen neatly along ideological lines.

The Obama administration EPA also blocked the mine, but the Trump EPA reversed this move, and appeared to be on track to approve the mine. 

The Trump administration later reversed course after prominent conservatives including Donald Trump Jr. came out against it. Fox host Tucker Carlson also aired a segment critical of the project. 

It was ultimately blocked by the U.S. Army Corps of Engineers under the Trump administration which denied a permit for the project, citing Clean Water Act concerns, in 2020. Pebble had appealed that decision. 

The project was the source of additional controversy after activists published secretly recorded tapes of executives of companies behind the mining project in which they suggested that the mine could be open for a longer time than what they had proposed and bragged about closeness with government officials. 

The Biden administration’s move was celebrated by some environmental and tribal organizations. 

“Our ancestral responsibility to safeguard our watershed and fishery has united all of us in our work to defend the world’s last great wild salmon fishery. Today’s announcement is historic progress towards that goal,” Alannah Hurley, the executive director of United Tribes of Bristol Bay, which opposes the mine, told reporters.