Sulfide-Ore Copper Mining and the Risks
Sulfide mining poses a significant threat to Minnesota’s coldwater fisheries and native lake and brook trout. The watersheds in northeastern Minnesota, including the Boundary Waters Canoe Area Wilderness and Lake Superior tributaries, are interconnected and highly sensitive. Even small-scale contamination can spread widely, affecting fish populations far downstream.
Twin Metals, owned by Chilean mining giant Antofagasta, wants to build a copper-nickel mine immediately upstream of the Boundary Waters, and along waterways that flow into the Wilderness.
- Acid Mine Drainage from these mines would pollute the waterways that flow into and through the heart of the Boundary Waters and along the international border, downstream to Voyageurs National Park, Quetico Provincial Park, and Hudson Bay.
- This type of mining, hardrock mining, is America’s most toxic industry (EPA Toxic Release Inventory)
- Byproducts of sulfide-ore copper mining include hazardous pollutants such as sulfuric acid and heavy metals, which are harmful to wildlife and people, and could permanently ruin the pristine water and unspoiled forests of the Boundary Waters.
- An industrial mining district on the edge of the Boundary Waters would forever change the area, devastate the Wilderness ecosystems, pristine waters, wildlife, and surrounding communities.
- This type of mining has never been done before in Minnesota and has never been done without polluting area ground and/or surface waters.
- Antofagasta, who owns Twin Metals Minnesota and several copper mines in Chile, has a terrible environmental and social track record.
- The copper mining industry has a long history of acid mine drainage and heavy metals leaching, with catastrophic environmental impacts, especially to water.
The Boundary Waters Canoe Area Wilderness (BWCAW), one of the most visited wilderness areas in the U.S., has faced growing threats from sulfide-ore copper mining proposals since the early 2000s.
2000s–2010s: Interest in mining for copper, nickel, and other metals near the BWCAW increased due to rising global demand. Twin Metals, a subsidiary of Chilean mining giant Antofagasta, proposed a large underground mine just outside the wilderness boundary, within the Rainy River watershed that flows directly into the BWCAW.
2016: The Obama administration denied the renewal of Twin Metals’ federal mineral leases and began a two-year environmental study to consider a 20-year mining ban on 225,000 acres of public land near the BWCAW.
2017–2020: Under the Trump administration, those leases were reinstated, and the environmental study was canceled before completion. The move reignited widespread concern from scientists, local businesses, and conservation groups.
2021–2023: The Biden administration reversed course again — canceling Twin Metals’ leases in 2022 and completing the previously halted environmental review. In January 2023, the U.S. Department of the Interior issued a 20-year moratorium on new mining activity in the watershed surrounding the BWCAW.
2024–2025: Despite the moratorium, political efforts are underway to reverse these protections. Pro-mining legislation and conservative policy platforms threaten to reinstate leases and fast-track mining near the wilderness, keeping the future of the BWCAW uncertain.
The Boundary Waters Canoe Area Wilderness (BWCAW) faces escalating threats from proposed sulfide-ore copper mining projects, particularly those by Twin Metals Minnesota. Despite a 20-year federal mining moratorium enacted in 2023, recent political developments have aimed to dismantle these protections.
Legislative and Administrative Challenges
House Legislation: The U.S. House approved a bill that would lift the mining ban in the Superior National Forest and reinstate previously canceled mineral leases for Twin Metals. It would also prohibit review by the judicial branch, Forest Service and general public (but give those rights to mining companies). It is now moving onto the Senate.
Project 2025: This conservative policy agenda advocates for overturning the 20-year mining ban, promoting expedited permitting processes, and limiting judicial reviews of mining projects .
Executive Actions: The current administration has signaled intentions to reverse the mineral withdrawal, potentially through executive orders, undermining the scientific assessments that led to the original protections .
Why is Minnesota Trout Unlimited concerned?
Fish & Their Prey Directly at Risk
• Exposing sulfide minerals in ore, waste rock and mine pit walls to air and water generates acid mine drainage (AMD), which contains sulfuric acid, heavy metals(such as copper, zinc and mercury) and sulfates.
• Spills and seepage from surface storage of waste rock, underground mine pits, tailings pipelines or other facilities would release AMD to the interconnected streams, lakes, wetlands and groundwater flowing to the Boundary Waters.
• High acidity can alter gill membranes, prevent fish from breathing, and alter reproductive success.
• Copper, mercury and other metals in AMD are toxic to fish and the insects they eat over the short and long term.
• Sulfates increase the rate of mercury methylation in aquatic environments, leading to more frequent and more serious fish consumption advisories for high mercury content.
Fishing Opportunities Impacted
• Noise, dust and light pollution from 24-hour-a-day, 365-day-a-year mining operations would affect animal behavior and the quiet fishing experience.
• Mine infrastructure and additional road traffic would lead to forest fragmentation, which disrupts wildlife travel corridors and accelerates the spread of weedy invasive species, which change the forest character.
• Impacts from forest fragmentation would affect the forest and wildlife within it.
• Mining companies often restrict access to public lands used for mining operations, thus restricting hunting and fishing access previously enjoyed on Superior National Forest land near the Boundary Waters.
What actions can you take?
The U.S. House passed its version of the Reconciliation Bill on May 22, 2025 that includes dismantling Boundary Waters protections from sulfide-ore copper mining. This measure is a matter of policy, not budget and these efforts open the door to toxic copper mining within the watershed of the Boundary Waters, a world-class recreational fishery and home to native lake trout that are sensitive to small changes in the ecosystem.
Take action here or use the information below to call your Senator!
Find your US Senator here
Contact your Senators today and tell them:
Hi, I am calling for Senator_______
My name is_____________, and I live in____________(state).
The House version of the Reconciliation Bill dismantles Boundary Waters protections from sulfide-ore copper mining. This effort is a matter of policy, not budget. As your constituent and an angler, I ask that you remove language from the Reconciliation Bill that would open the door to toxic copper mining within the watershed of the Boundary Waters – America’s most visited Wilderness. This habitat supports world-class recreational fisheries that are sensitive to small changes in the ecosystem. Please ensure that hard-won protections are not rolled back by opposing any budget reconciliation efforts that would harm the Boundary Waters.
Thank you.
Learn More
You can read about fly fishing the Boundary Waters in this article from our 2017 Trout Unlimited Minnesota newsletter, Lake Trout in the Boundary Waters and mining in our 2018 newsletter.
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