Clark Fork River Named Among America’s Most Endangered Rivers of 2023

April 18, 2023


Lisa Ronald, Western Montana Associate Conservation Director, American Rivers, 406-317-7757 
Karen Knudsen, Executive Director, Clark Fork Coalition 

American Rivers has named the Clark Fork River among America’s Most Endangered Rivers®, citing industrial pollution from a shuttered pulp mill that threatens the river’s recovery from a hard-working past. The Clark Fork flows more than 300 miles through an area of ancestral and continuing importance to the Salish and Kalispel peoples. The river supplies habitat for diverse fish and wildlife species and drinking water and irrigation for local communities. It is the engine of the region’s agricultural and outdoor economies.  

Today, the defunct Smurfit-Stone pulp mill and its unlined and unsafe waste dumps sit downstream of Missoula in the Clark Fork’s active floodplain, leaking toxic chemicals and heavy metals into groundwater that is connected to the river. Fish in this reach of the Clark Fork are considered too contaminated to safely consume.  And although the mill has been closed for 13 years, and International Paper and WestRock are financially responsible for the costs of cleanup, the Environmental Protection Agency (EPA) has yet to tackle the problem – despite compelling evidence that cleanup of the most contaminated part of the site should start immediately.  

“Missoula, downstream communities, and the Confederated Salish and Kootenai Tribes deserve clean water and edible fish. Cleaning up Smurfit-Stone is not just the right thing to do, it’s a smart economic decision since cleanup now is less expensive than cleanup after a disaster,” said American Rivers Western Montana Associate Conservation Director Lisa Ronald.  

Forming the eastern headwaters of the Columbia Basin, the Clark Fork is Montana’s largest river by volume. It rises out of mountains along the Continental Divide near Butte and captures water from 28,000 miles of creeks and streams on its journey to Idaho’s largest natural lake, Lake Pend Oreille. It is a regional boating and angling destination and is home to native westslope cutthroat trout and threatened bull trout. 

“The Clark Fork River is in the heart of our ancestral homelands, but it’s like being punched in the gut when you have something like Smurfit in that location. We want to restore the floodplain, reclaim lost pieces of our culture, and honor our treaty and our ancestors,” said Council Chairman for the Confederated Salish and Kootenai Tribes Tom McDonald. 

Between 1957 and 2010, the Smurfit-Stone pulp mill created pulp from woodchips and then produced rolls of kraft linerboard for cardboard boxes, some of which it bleached. The process generated a tremendous amount of chemicals and hazardous substances, which were either discharged directly into the Clark Fork, held temporarily in riverside settling ponds, or buried in unlined sludge ponds, waste dumps, and landfills. These waste management areas span roughly 1,000 acres of the site, though it’s the roughly 140 acres of buried sludge and industrial refuse that make up the most acutely problematic part of the site. 

The rest of the waste management area – the 900 acres of settling ponds – are separated from the Clark Fork River by an unengineered, unpermitted gravel berm. Because it hasn’t been maintained since the mill shuttered in 2010, annual spring runoff and periodic flooding continue to erode the berm each year. A catastrophic flood, such as one like the Yellowstone River flood of 2022, would likely fully inundate or collapse the berm and pull industrial pollutants into the river and downstream.  

“One of the biggest environmental concerns we have is that there will be a 100-year, 300-year, or 500-year flood that will take out the berms and potentially create a colossal catastrophic environmental nightmare in the Clark Fork drainage and watershed,” said Missoula County Commissioner Dave Strohmaier. “Right now, the berms are the only line of defense that keeps the Clark Fork River under extreme flood conditions from scouring out contaminants.” 

To prevent catastrophic flooding and ongoing pollution of groundwater that’s connected to the river, the EPA must should direct International Paper and WestRock to clean up the roughly 140 acres of contaminated waste dumps. Additionally, EPA should conduct supplemental groundwater, soil, and wildlife exposure testing to better characterize the source and pathways of pollutants and develop a thorough and comprehensive cleanup that results in a river that is reconnected with its floodplain. The EPA has the authority through the Superfund process to require these cleanup actions. 

“The Clark Fork Coalition and many others have worked hard to heal the scars of the Clark Fork River’s hardworking past, but a major wrench in recovery is the shuttered Smurfit-Stone mill,” said Executive Director of the Clark Fork Coalition Karen Knudsen. “Our community wants to do right by its river. It’s been 13 years since the Smurfit-Stone mill closed, and the time for cleanup is now.” 

The annual America’s Most Endangered Rivers report is a list of rivers at a crossroads, where key decisions in the coming months will determine the rivers’ fates. Over the years, the report has helped spur many successes including the removal of outdated dams, the protection of rivers with Wild and Scenic designations, and the prevention of harmful development and pollution. 

Other rivers in the region listed as most endangered in past years include the Smith River (2018 & 2016), Middle Fork Flathead River (2017) and Kootenai River (2013).

America’s Most Endangered Rivers® of 2023  

  1. Colorado River, Grand Canyon (Arizona):  

THREAT: Climate change, outdated water management  
AT RISK: Ecosystem health, reliable water delivery, regional economy  

  1. Ohio River (Pennsylvania, Ohio, West Virginia, Kentucky, Indiana, Illinois):  

THREAT: Pollution, climate change  
AT RISK: Clean water for 5 million people  

  1. Pearl River (Mississippi):  

THREAT: Dredging and dam construction  
AT RISK: Clean drinking water, local and downstream communities, fish and wildlife habitat  

  1. Snake River (Idaho, Oregon, Washington):  

THREAT: Four federal dams  
AT RISK: Tribal treaty rights and culture, endangered salmon runs, rural and local communities  

  1. Clark Fork River (Montana):  

THREAT: Pulp mill pollution  
AT RISK: Public health, fish and wildlife  

  1. Eel River (California):  

THREAT: Dams  
AT RISK: Fish and wildlife, tribal culture and sustenance  

  1. Lehigh River (Pennsylvania):  

THREAT: Poorly planned development  
AT RISK: Clean water, fish and wildlife habitat, rural and local communities, open space  

  1. Chilkat and Klehini rivers (Alaska):  

THREAT: Mining  
AT RISK: Bald eagle, fish, and wildlife habitat, tribal culture and sustenance  

  1. Rio Gallinas (New Mexico):  

THREAT: Climate change, outdated forest and watershed management  
AT RISK: Clean drinking water, farming, watershed functionality  

  1. Okefenokee Swamp (Georgia, Florida):  

THREAT: Mining  
AT RISK: Fish and wildlife habitat, wetlands, water quality and flow

About American Rivers  
American Rivers is championing a national effort to protect and restore all rivers, from remote mountain streams to urban waterways. Healthy rivers provide people and nature with clean, abundant water and natural habitat. For 50 years, American Rivers staff, supporters, and partners have shared a common belief: Life Depends on Rivers. For more information, please visit