Experts began studying mine waste along the Clark Fork after heavy rain pushed it into the river Friday, Sept. 6, killing hundreds of fish.

“There’s stuff out there that’s killing fish that’s not good for people,” said Alex Leone, restoration and policy manager at the Clark Fork Coalition.

Leone said 32 dead trout, whitefish and suckers were discovered on Monday, Sept. 9. He assumed many were eaten by wildlife or swept downstream by the time they investigated. They found the highest concentration of dead fish near spilled slickens, or areas of built-up mine waste along the Clark Fork. He estimated that hundreds of fish had died.

The waste settled in the upper Clark Fork in 1908, when extreme flooding washed piles of crushed mine material down the river. The Atlantic Richfield Company, the oil company responsible for the waste, built berms to prevent the slickens from washing into the river after several fish kills occurred in the 1980s and 1990s, according to Leone. On Friday, Sept. 6, heavy rain pressured the roughly 30-year-old berms to the breaking point, allowing the blue-green water with high concentrations of copper and arsenic to flow into the river.


A dead fish floats in the Clark Fork river near Warm Springs. Officials estimated that hundreds of fish died after heavy rain pushed mine waste into the river on Friday, Sept. 6, 2019. 32 dead trout, whitefish, and suckers were found when they checked. 

“It’s like a bathtub filled up and somebody pulled the plug,” Leone said.

Nathan Cook, fisheries biologist with Montana Fish, Wildlife and Parks, said that the berms worked well until a few years ago. He said there were flow trails from the slickens to the river and obvious areas where blue sediment had built up on the riverbed and on rocks. High levels of copper can slow fish growth and increase mortality, Cook said.

“This event really highlighted that there’s still the potential out there for these catastrophic effects,” Cook said.“It made me think about it in a different way; it added a little urgency to the cleanup.”

Cook said the presence of the slickens holds future risks as well. The area where the fish kill occurred and where the most slickens are located is between Perkins Lane and Galen Street Bridge near Warm Springs, Cook said. Maury Valett, a freshwater ecosystems ecologist and professor at UM, and a group of students are studying the impact of the waste on the whole river.

“Even if the metals aren’t killing fish, it’s messing with the environment the fish need to live in,” Valett said.

Valett works with the Consortium for Research on Environmental Water Systems (CREWS.) This group is studying the way metals in the slickens travel through the ecosystem. Bug population numbers drop after being exposed to this kind of spill. Eating bugs that have consumed biofilms containing dangerous metals can harm fish. There is also little to no plant growth in these slickens because of the soil conditions.

“In some cases, the metals concentrations are so high that you could easily mine that soil,” Valett said.

Leone said the cleanup process is tedious. It involves removing the slickens and the soil beneath them, replacing the contaminated soil with new material and then beginning the vegetation and shade restoration process. He hopes the construction portion near where the fish kill occurred can begin soon.

“We want to make sure they start cleaning up this area where the fish kill happened next year,” he said. “This is too big of a deal to wait.”

This project will include 40 miles of cleanup in and along the Clark Fork before it reaches Missoula. The Clark Fork, after meeting with the Blackfoot, Bitterroot and Flathead rivers, is a major headwater of the Columbia River, one of the largest rivers in the country.

“They’ve never done a river cleanup at this scale anywhere in the world that we know,” Leone said. “The water, the mountains and the animals. It’s just the core of our world,” Valett said. “I don’t think there’s a Montanan that doesn’t think we should deal with this.”


The Clark Fork River passes through Missoula near Caras Park. The river is heavily trafficked with floaters during the summer, raising concerns about litter and pollution.