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Massive Canadian mines pose transboundary risks

Science Magazine

In 2019, Canada approved an extension of the deadline to start one of the world’s largest copper and gold mines in the headwaters of the transboundary Unuk River (1). The plan for the Kerr-Sulphurets -Mitchell (KSM) mine is to dig one of the largest human-made holes on earth, erect one of the highest dams in North America, and operate water treatment for 200 years after the mine closes (2). Mines such as KSM pose long-term risks to downstream water quality, fish, and people (3). Given that mine contamination is not constrained by political boundaries, U.S., Canadian, and Indigenous governments must urgently engage in collaborative evaluation and regulation of mines in internationally shared rivers. Shortfalls in mine assessments and permitting policies should be addressed.
Mine assessments underestimate risk at high environmental cost. Contributing factors include the ecological complexity of rivers, policy shortcomings in weighing environmental risk (4), and profound engineering challenges posed by mountain mining. For example, insufficient evaluation of soil stability enabled the 2014 catastrophic failure of the Mount Polley tailings dam (5).
Furthermore, the issuance of mine permits relies on the promise of mitigations that lack field validation. Canadian industrial projects typically underdeliver on their mitigations, such as restoring fish habitat (6). Unverified technologies can fail, as evidenced by the 2014 fish kill downstream of Teck Resources’ wastewater treatment plant (7).
Finally, mine assessment and permitting do not require incorporation of transparent, independent, and peer-reviewed science (8). For example, Teck’s Elk Valley permit allows contaminant discharges up to 65 times above scientifically established protective thresholds for fish (9). Political borders do not block the downstream flow of this contaminated water into Montana and Idaho (10).
Stakes are high. Upstream Canadian mines threaten downstream economies, waters, and ways of life, even as the United States is currently weakening its own federal environmental regulations (11). Rather than a race to the bottom, we urge our governments to honor their mutual obligations to protect our shared transboundary waters as codified in the Boundary Waters Treaty of 1909 (12) and immediately collaborate on binational environmental reviews that are founded upon independent, transparent, and peer-reviewed science.

Erin K. Sexton 1 , Christopher J. Sergeant 1,2, Jonathan W. Moore 3, Alana R. Westwood 4, David M. Chambers 5, Megan V. McPhee 2, Sonia A. Nagorski 6, Sarah L. O’Neal 7, Jill Weitz 8, Adrienne Berchtold 9, Marissa Capito 10, Christopher. A. Frissell 1,11, Jennifer Hamblen 12, F. Richard Hauer 1, Leslie A. Jones 13, Greg Knox 9, Randal Macnair 14, Rachel L. Malison 1, Vicki Marlatt 15, Jennifer McIntyre 16, Nikki Skuce 17, Diane C. Whited 1

C.A.F. is affiliated with the Department of Hydrology Salish Kootenai College, Pablo, MT 59855, USA. S.L.O. is affiliated with Agua Dulce Freshwater Consulting. A.R.W. is affiliated with Natural Resources Canada, but the views expressed herein do not in any way represent the Government of Canada or its departments or agencies.
1Flathead Lake Biological Station, University of Montana, Polson, MT 59860, USA.
2College of Fisheries and Ocean Sciences, University of Alaska Fairbanks, Juneau, AK 99801, USA.
3Earth2Ocean Research Group, Simon Fraser University, Burnaby, BC V5A 1S6, Canada.
4Mitacs Canadian Science Policy Fellow, Ottawa, ON K1P5A9, Canada.
5Center for Science in Public Participation, Bozeman, MT 59715, USA.
6Environmental Science and Geography Programs, University of Alaska Southeast, Juneau, AK 99801, USA.
7School of Aquatic and Fishery Sciences, University of Washington, Seattle, WA 98105, USA.
8Salmon Beyond Borders, Juneau, AK 99801, USA.
9SkeenaWild Conservation Trust, Terrace, BC V8G 1M9, Canada.
10Juneau, AK 99801, USA.
11Frissell and Raven Hydrobiological and Landscape Sciences LLC, Polson, MT 59860, USA.
12Takshanuk Watershed Council, Haines, AK 99827, USA.
13Alaska Center for Conservation Science, University of Alaska, Anchorage, Anchorage, AK 99508, USA.
14Wildsight, Kimberley, BC V1A 1Z6, Canada.
15Department of Biological Sciences, Simon Fraser University, BC V5A 1S6 Canada.
16School of the Environment, Puyallup Research and Extension Center, Washington State University, WA 98371, USA.
17Northern Confluence Initiative, Smithers, BC V0J 2N0, Canada. ∗Corresponding author. Email:


2. H. Ghaffari et al., “KSM (Kerr-Sulphurets-Mitchell) prefeasibility study update and preliminary economic assessment,” Tetra Tech (2016);
3. M. A. Palmer et al., Science 327, 148 (2010).
4. C. C. Murray et al., Environ. Manage61, 1062 (2018).
5. Independent Expert Engineering Investigation and Review Panel, “Report on Mount Polley Tailings Storage Facility Breach” (2015);
6. J. T. Quigley, D. J. Harper, Environ. Manage37, 336 (2006).
7. Government of Canada, “Teck Coal Limited: Conviction information for 2017-10-05” (2017);
8. A. R. Westwood et al., UBC Law Rev52, 243 (2019).
9. Teck, “Elk Valley Water Quality Plan,” Teck Coal Limited (Sparwood, BC, 2014);
10. T. S. Presser et al., “USGS measurements of dissolved and suspended particulate material selenium in Lake Koocanusa in the vicinity of Libby Dam (MT), 2015–2017 (update)” (U.S. Geological Survey data release, 2018).
11. A. Wittenberg, Science, 10.1126/science.aan7035 (2017).
12. The Boundary Waters Treaty of 1909 (International Joint Commission, 2016);


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