The Trump administration is planning to block the controversial Pebble Mine in southwestern Alaska that’s recently drawn opposition from certain powerful Republicans, according to a person familiar with the matter.

The project, which has known deposits of copper, gold and other metals, is located in an area that drains into Bristol Bay, home to the world’s most productive wild salmon fishery.

Conservationists, local activists and fishing operations have fought the project for years, but blocking the project would be a reversal for the Trump administration.

The Environmental Protection Agency in 2019 resumed consideration of the proposed water pollution restrictions that had effectively stalled the project since they were outlined in 2014. In July, Pebble Mine secured a final environmental impact review from the US Army Corps of Engineers, regarded as a major step toward permitting and production.

The Corps is said to be sending a letter to the mine noting that the project may pose significant environmental degradation. While that doesn’t spell the absolute end of the road for the project, it’s a signal that a lot more work may be required before a permit would be granted -- a move that could push a final decision on the project until after the November election.

The Pebble Limited Partnership, which is owned by a Canadian subsidiary of Northern Dynasty Minerals, downplayed the development, saying “it appears that the normal process continues to move forward for the project.”

“We categorically deny any reports that the Trump Administration is going to return to an Obama-like approach that allowed politics to interfere with the normal, traditional permitting process,” Pebble Mine CEO Tom Collier said in a statement. “This president clearly believes in keeping politics out of permitting -- something conservatives and the business community fully support.”

Politico first reported on the reversal of fortune for the Pebble Mine on Saturday.

A representative of the Interior Department referred inquiries to the Army Corps, which didn’t respond to requests for comment.

Donald Trump Jr., the president’s son and a keen sportsman, took to Twitter this month to oppose the mining project, lining up with Nick Ayers, a former chief of staff to Vice President Mike Pence.

“The headwaters of Bristol Bay and the surrounding fishery are too unique and fragile to take any chances with,” Trump Jr. wrote.

The decision to halt or at least slow-walk the mine, while not confirmed, already won applause from environmentalists.

“Stopping Pebble Mine was the right decision by the Obama administration in 2014 and we thank the Trump administration for making the right decision today,” said Collin O’Mara, president and CEO of the National Wildlife Federation. “This decision marks a key step to save Alaska’s Bristol Bay.”

The National Mining Association said in a statement on Saturday that it was unaware of any action by the Trump administration but that blocking the mine “would be an unfortunate return to science taking a back seat to politics.”