Boundary Waters is the most heavily visited wilderness area in the country, according to the Interior Department. And Thursday’s decision will affect 225,000 acres of federal lands and waters in the Rainy River Watershed, which abuts the wilderness area northwest of Lake Superior.

It comes a day after the administration took action to protect Alaska’s Tongass National Forest, and as it faces other decisions on hotly fought over sites in Alaska and Nevada. The Biden administration has promised to set aside sacred tribal sites and to conserve 30 percent of America’s lands and waters by 2030, but has come under fire for how to balance that push with demand for oil, renewable energy and minerals.

“The Department of the Interior takes seriously our obligations to steward public lands and waters on behalf of all Americans,” Interior Secretary Deb Haaland said in a statement. “Protecting a place like Boundary Waters is key to supporting the health of the watershed and its surrounding wildlife, upholding our Tribal trust and treaty responsibilities, and boosting the local recreation economy.”

Advocates for mining in the region have said it can be a key domestic source of the materials needed for President Biden’s promised transition to cleaner energy. Twin Metals Minnesota, a subsidiary of the Chilean mining conglomerate Antofagasta, held leases there that the administration canceled last year, and has accused the administration of trying to go around the law to stop the project for political gain.

In a statement Thursday, a mining industry leader said the decision was frustrating, given the Biden administration’s stated goals on “electrification, the energy transition and supply chain security.”

“At a time when demand for minerals such as copper, nickel and cobalt are skyrocketing for use in electric vehicles and solar and wind infrastructure, the administration is withdrawing hundreds of thousands of acres of land that could provide U.S. manufacturers with plentiful sources of these same minerals,” said Rich Nolan, president and chief executive of the National Mining Association.

The administration’s environmental agenda has led to similar showdowns with oil and mining companies in Alaska and solar developers in Nevada. It faces decisions many expect within days on the Bristol Bay watershed in Alaska and 33,000 acres around the Avi Kwa Ame mountain in Nevada.

It also made a commitment to Alaskan leaders to finish an environmental review this month on ConocoPhillips’s multibillion-dollar Willow oil project, which climate activists oppose. That deadline arrives Tuesday, and the administration has signaled it may allow drilling to go forward there, within a smaller area.

Current and former administration officials think the company’s long-standing leases would be hard for the federal government to break. Such legal impediments have forced the administration to go slow on big swaths of its climate agenda and limited how far it can go to fulfill promises Biden has made to block oil drilling in the Arctic and other federal territory.

“They have had legitimate difficulties with a divided country and Congress,” said John Leshy, a law professor who served as Interior’s solicitor under President Bill Clinton and has written on federal authority to curb fossil fuel leasing. “They are exhorting people — in state government, in the private sector, at all levels — to pay more attention to conservation. I think that is generally working.”

Biden commits to honoring tribes by protecting public lands in Nevada

Administration officials did not take questions on the timing of their moves and whether there is a strategy to expedite them now. But in recent days they have emphasized they are committed to fulfilling the environmental promises Biden made at the start of his administration.

On Thursday, an Interior official noted the department had already canceled the Twin Metals leases, clearing an easier path for Haaland to order protections around the 1.1 million acres of Boundary Waters to go into effect. It had said the leases were improperly renewed under the Trump administration through an inadequate environmental analysis that had sidestepped the U.S. Forest Service, which manages the surface area.

Senior officials at the department see the wilderness there as a unique place, “irreplaceable” and easily damaged because of the immense and fragile connections between all the waterways that pockmark the region. In 2021, the Biden administration launched a scientific analysis, which found mining could cause irreparable damage to the region’s nature and culture, officials said Thursday. It found several examples in the last decade where containment efforts failed and other leaks from mines in the region caused such damage, an Agriculture Department official said.

Each year, Boundary Waters attracts roughly 150,000 Boy Scouts and other visitors looking to canoe, fish and connect with nature. The glaciers that gouged the region over the past 2 million years left behind a rugged terrain that is now home to wolves, moose, bobcats, beavers, bald eagles and peregrine falcons.

“Acid pollution from sulfide mines as far away as 100 miles threaten the park’s waters and all who visit. Even small amounts of this pollution is detrimental to public health,” Christine Goepfert, campaign director for the National Parks Conservation Association, said in a statement. “Banning mining activities in the region’s prized Boundary Waters will protect the broader park ecosystem now and for years to come.”