These animals endanger Idaho rivers. Getting rid of them is a ‘massive puzzle’
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- Idaho treated a stretch of the Snake River with copper to eradicate quagga mussels.
- Teams refined methods under uncertainty while other states and provinces observe.
- Copper treatment ran 24/7 with daily water samples.
At lunch on Friday, two Idaho officials, a project engineer and an invasive species expert, walked along the shore of the Snake River, eating hard-won slices of pizza. They’d been at the bottom of the canyon near the Twin Falls Dam for two weeks, often working 18-hour days in the state’s fight against quagga mussels that had invaded the moving waters.
The pizza was a fitting celebration for the end of a 200-hour period of treating the river with a copper solution to eradicate the mussels. The treatment is a 24/7 undertaking that — for project leaders Jeremey Varley, the chief treatment engineer for the Idaho Department of Agriculture, and Nic Zurfluh, the department’s bureau chief of invasive species, noxious weeds and range programs — brought nights sleeping in the backs of their trucks and workdays that began at dawn and ended near midnight. By the end of it, the two were “attached at the hip,” Varley said.
On a boat tour of the treatment area, Varley and Zurfluh told the Statesman that eradicating the mussels requires constant calibration of the copper levels in the water, a complicated task that demands everything from scuba dives to dozens of water samples each day.
It’s the third year in a row that Idaho has been fighting the mussels, which were first detected in the river in 2023. Left unchecked, and with no natural predators in Idaho waters, the mussels threaten to overeat the river’s plankton, “collapsing the bottom end of the food web” that other native organisms rely on, Varley said.
With time, the mussels would cling to and clog up surfaces like irrigation pipes and hydroelectric equipment, threatening serious damage to Idaho agriculture and power projects.
The state last year managed to reduce the mussels’ presence, Varley said, shrinking the number of infested miles by half. It was an “unheard-of” success rate in targeting invasive species, he said, but it brought a challenge in this year’s efforts to go after areas where mussels were still detected.
“As you get closer and closer to zero with any invasive species, the harder and harder it gets because they’re spread out or hard to find,” Zurfluh said. “Think of weeding out your garden. If you have a whole garden, you’re like, ‘OK, I can just start tackling it.’ But how hard is it to find the last weed?”
The state has taken an aggressive, eradication-focused approach, Varley and Zurfluh said. But taking on the mussels is a delicate task. The team wants a small concentration of copper — about 1 part per million — in the sections of the river under treatment. That’s no easy feat in constantly flowing water, with deep holes in the riverbed and marshy areas along the shoreline providing the mussels with refuge from the poison. It’s an environment where such treatment has never been done before.
They also have to make sure the copper lingers long enough in any one spot for mussels to ingest a fatal dose.
“They’re kind of like your kid with broccoli,” Varley said. “They’re going to open their mouth. They’re going to taste it. They don’t like it. They close back up, hold their breath. And so it’s these micro-doses they’re taking.”
Focused in now on a narrow stretch of the Snake River, from Shoshone Falls through the Twin Falls Dam, the team said it hopes it’s the last time they’ll have to treat the river. The treatment has cost millions of dollars, and it eradicated most of the invertebrates in the affected area, according to a U.S. Geological Survey of the first treatment in 2023.
The destruction of up to 90% of the invertebrates living in the area put at stake food resources for future fish populations in the river, the study found, and it was unclear how long those effects would last. Over 7,000 pounds of copper also settled into the riverbed, according to the study, potentially remaining toxic, the Statesman previously reported.
But the state chose “the lesser of two evils,” Zurfluh said. Left untreated, the mussels themselves would have devastated the ecosystem, and would have multiplied with each passing year, becoming more expensive and complicated to eradicate. And they likely would have spread into other bodies of water.
“We’re essentially treating 1% of the Snake River —” Zurfluh started.
“To save the entire Columbia basin,” Varley finished, as the boat traveled in the shadow of looming canyon walls.
‘No instructions’ on how to fight mussels in rivers
Originally from the Black and Caspian seas, quagga mussels first made their way to the U.S. in the 1980s. Back home, they’re kept in check by natural predators, but as they’ve cropped up in lakes around the country, it’s had devastating effects.
Until now, the mussels had never made it into rivers, at least not at the scale they were observed in the Snake River, Zurfluh and Varley said.
So the pair is learning in real time how to take on the mussels on in this new environment, refining their approach to eradicating the mussels each year of treatment.
“You have this massive puzzle here, and now you’ve got to take all these pieces and put them together,” Zurfluh said. “But you have no instructions, nor do you know how many pieces of the puzzle there actually are.”
At first, the team focused on just getting the copper solution into the river, but they’ve learned to account for the influx of fresh water coming in midstream from springs and irrigation runoff. They’ve begun treating marshy areas along the shoreline where copper had been absorbing into the soil without reaching the water. And they’ve developed underwater fans to help hold the copper mixture in suspension at all river depths.
“It’s almost like Italian dressing,” Varley said. “When you shake it, you want it to stay in suspension. You don’t want everything to drop.”
Other local governments are watching, from Washington and Oregon to British Columbia and Alberta, and several officials have toured the Snake River treatment sites to report back to their home agencies.
“We are figuring this out for everyone, and there’s been a lot of eyes on this,” Chanel Tewalt, the director of the Department of Agriculture, previously told the Statesman.
Soon after wrapping up its treatment, the team will gather to talk through any areas it may have missed and establish a plan for tackling those next year, if more mussels are detected. They won’t know until next summer if they succeeded, but they’ve treated each round of treatment as the last, Zurfluh and Varley said.
“The game is not over. We’re still going to keep after it,” Varley said. But “we really wanted to make sure we left no cards left on the table after we were done.”
This story was originally published October 14, 2025 at 12:22 PM.
