The Biden administration took a major legal step towards protecting Bristol Bay in Alaska, one of the world's most valuable sockeye salmon fisheries that also sits atop enormous copper and gold deposits.

The EPA proposed a legal determination that would ban the disposal of mining waste in the Bristol Bay Watershed. The move could deal a death blow to the proposed Pebble Mine, an intensely disputed project that would have removed the metals but also irreparably harmed the environment.

The proposal to create permanent protections for the waters and wildlife of Bristol Bay will be finalized later this year.

The determination would prohibit any entity from disposing of mine-related waste in the vicinity of the proposed Pebble Mine project. That area is four times larger than Washington, D.C., but just a small portion of the entire Bristol Bay Watershed.

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The administrator of the Environmental Protection Agency said that the Bristol Bay Watershed is a shining example of how our nation's waters are essential to healthy communities.

President Biden promised on the campaign trail to listen to the scientists and protect Bristol Bay if he were elected.

Mr. Biden said that the region was not a place for a mine.

The fight over the fate of Bristol Bay has been going on for more than a decade. The plan to mine Bristol Bay was scuttled by the Obama administration, but found new life under President Trump. Donald Trump Jr., a sportsman who had fished in the region, came out against the project. The waters are full of salmon.

The project was denied a permit by the Army Corps of Engineers in 2020.

The company that wants to build the mine appealed the decision and is expected to challenge the legality of the Biden administration's plan to protect Bristol Bay.

The company wants to dig an open-pit mine more than a mile square and one-third of a mile deep where it would process tens of millions of tons of rock a year to extract metals estimated to be worth at least $300 billion. The project would include the construction of a 270-megawatt power plant and 165-mile natural-gas line, as well as an 81-mile road and large dammed ponds, some of them toxic. Iliamna Bay would need to be dredged.

The breeding grounds for salmon that are the basis for a sport fishing industry and a large commercial fishery in Bristol Bay would be damaged by the proposed Pebble Mine, according to both federal and state agencies. Salmon is an important part of the diet of Alaska Natives who live in small villages. More than 130 miles of streams, 2,800 acres of wetlands and 130 acres of open water would be destroyed by the mine, according to scientists.

A spokesman for the Pebble Mine Partnership said last fall that blocking the project could have a negative effect on the Biden administration's goals to combat climate change.

As the Biden Administration seeks to lower carbon emissions for energy production, they should be aware of the need for more mineral production, said Mike Heatwole in a statement.

There is significant economic value in Bristol Bay according to the Biden administration. The E.P.A. found that the Bristol Bay commercial salmon fishery created 15,000 jobs and generated $2 billion in economic activity in 2019.

The final legal determination on the proposal will be published on July 5.