Idaho to treat Snake River again in ‘aggressive’ fight against quagga mussels

BOISE (Idaho Statesman)

– Idaho state officials this fall plan to continue treatments to eradicate quagga mussels, an invasive species threatening the state’s ecosystem, after they found larvae remaining in the Snake River, but celebrated results that showed they shrank the infested area by half.

Idaho spent $3 million the past two years on copper poisoning to treat the Snake River, just enough of a concentration to kill off the invasive species and still under the limit for drinking water.

The state initially found 7 miles of the river near Twin Falls infested with veligers, state officials said, which are quagga mussel larvae before they turn into adult mussels.

From Centennial Park to Shoshone Falls, two segments of the river — divided by Pillar Falls — tested quagga mussel-free this year, officials said.

“There’s never been a treatment of this scale,” let alone one that was successful, Chanel Tewalt, director of the department, told the Idaho Statesman on Friday. “We are figuring this out for everyone, and there’s been a lot of eyes on this.”

The state has been using copper poisoning that is the industry standard for treating water for quagga mussels. State officials said the invasive species posed a unique challenge in the Snake River, though.

Such treatments had never been used in moving water before, officials previously told the Statesman.

A U.S. Geological Survey study showed that the 2023 treatments eradicated most of the invertebrate living in the affected area, which fish rely on for food, the Statesman previously reported.

The study also concluded that potentially toxic copper also settled into the riverbed. After 2024 treatments, the state saw the impact mostly on carp and sucker fish, spokesperson Sydney Kennedy told the Statesman.

Tewalt had emphasized that there would have been “collateral either way,” and that choosing not to treat the quagga mussels would have devastated the ecosystem.

Two other river segments, from Shoshone Falls through the Twin Falls Dam, remain infested, and state officials said they plan to continue their fight against the species with more copper treatments concentrated in the affected areas.

Tewalt said they’re also exploring other options that could improve their methods, including underwater fans that help push the copper toward affected areas, and using more experts to weigh in on their treatments.

Several companies, agriculture industry officials and conservation advocates in the news release emphasized the devastating impacts the species would have the mussels took over the Snake River. They applauded the state’s “aggressive” efforts and found the findings encouraging.

“Idaho’s water is the backbone of our communities, economies, and agricultural success,” said Paul Arrington, executive director of the Idaho Water Users Association. “Quagga mussels threaten that lifeline. … The recent findings highlight the urgent need for continued, aggressive response.”

In the news release, stakeholders urged the state to continue doing everything it can to fully eradicate the quagga mussels.

Bryan Searle, from the Idaho Farm Bureau Federation, called the reduction a “significant milestone” that shows real progress.

“At the same time, we know how devastating quagga mussels can be for Idaho agriculture,” Searle said. “We call on ISDA to do everything necessary to finish the job and reach eradication.”

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