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Official: Idaho Responded to Snake River Quaggas at 'Lightning Speed' by K.C. Mehaffey Northwest Fishletter, November 5, 2025

ISDA did not want to get stuck in "analysis paralysis,"
which can happen when faced with a difficult decision.

On Oct. 14, the Idaho State Department of Agriculture finished treating a section of the Snake River with chelated copper for the third year in a row, hoping to eradicate quagga mussels detected near Twin Falls, Idaho.

This time, the operation included deep-hole injections and shoreline treatments along with applying copper for 200 hours in the main-stem river in order to maintain a lethal concentration level for mussels but not people.

Compared to 2023 and 2024, the treatment area was roughly half as large, after water samples detected the presence of mussels only along a 3.5-mile stretch of the river from Sageview to Shoshone Falls.

And like prior years, the decision to treat the river with copper was made quickly, despite the knowledge that it would kill fish and other aquatic life, and close a popular Snake River recreation area that is also one of the biggest tourist areas in the state.

The day after completing this year's treatment, ISDA Director Chanel Tewalt explained the importance of Idaho's rapid response to the quagga mussel detection in a presentation to the Northwest Power and Conservation Council.

Tewalt pointed out that treating a large river with the intent of irradicating invasive mussels has never been done before. "So, there's no playbook for it," she said.

The decisions each year to treat the river with copper have been made quickly, but without cutting corners.

In September 2023, when the mussels were first detected in the Snake River, "From the time of detection to the time we got copper in the water was two weeks and one day, which is lightning speed," she said.

That included getting state and federal permitting, determining what product to use to kill the mussels, developing a technical plan for applying the copper, and conducting outreach with other agencies and the public.

"We just threw all the balls up in the air at the same time and juggled a lot," she said.

Tewalt said ISDA did not want to get stuck in "analysis paralysis," which can happen when faced with a difficult decision.

She noted that in Colorado, when invasive mussels were detected in a lake, it took six months before treatment began. In California, which is just beginning to treat for invasive golden mussels, it's been 18 months since detection.

"That's not to say that that process is wrong," she said.

However, "The decisions that you have to make on a treatment like this are not going to get more comfortable with time. And we knew that, and we were willing to just bite the bullet and take the arrows. We would rather be fast and effective than wait for everyone to be comfortable because that just simply wasn't going to happen," she told the Council.

Tewalt noted that from the very start, she had the full support of Idaho Gov. Brad Little, who was completely familiar with the importance of preventing quagga mussels from becoming established in the Columbia Basin. He also understood the potential impacts the mussels could have on the state's agriculture and hydroelectric generation, along with the Snake River ecosystem, she said.

She met with Little the same day ISDA confirmed the water sample detected a larval form of quagga mussels. "Within 30 minutes he had his chief of staff, [and] communications director in an all-cabinet meeting with every agency in the state, saying, 'This is a state priority,'" Tewalt said.

She also described how all of the players -- from state and federal agencies to technical experts and local leaders -- were able to agree on a plan so quickly.

ISDA took everyone involved out on boats to a location on the Snake River with a natural waterfall called Pillar Falls. "We got everyone off the boats, and literally, I held up the keys and I said nobody goes home and nobody gets fed until we come up with a plan," she said.

ISDA already had a plan, she said. "The point was for everyone to shoot arrows at it if they needed to. Give us their most constructive, harsh criticism. We talked about heavy metals and alkalinity, we talked about the product we were using, we talked about fish mortality. We talked about everything right there."

After everyone agreed to the plan, they held a town hall meeting two days before the treatments began. The meeting was open to the public and live streamed. ISDA invited media and took unscripted questions.

Tewalt said they were open, transparent and "audaciously" honest.

"We said, 'We are going to kill all the fish in this part of the Snake River.' There was no hyperbole about it. We were blunt. We were extremely honest: We would kill all the algae all the macrophytes, all the fish, and God willing all the mussels. And as hard as that is, as heartbreaking as that process will be, doing nothing is worse. Being slow is worse," she said.

Tewalt said in general -- she thinks because of the transparency -- media reports have been understanding of the agency's actions. When feedback has been critical, she said, ISDA has invited people to come see what they were doing, and why, and show them every aspect of the problem.

Tewalt credited her "small but mighty" staff for their ability to tolerate discomfort and their dedication.

She said as a public servant, she not only had to explain the importance of the treatment despite its consequences, but she had to live through it.

Tewalt recalled how difficult it was to be there during the first copper treatment in 2023, when they picked up the first dead fish.

"It's dark and you're right there under the waterfall and I can't tell you how poignant and heartbreaking that moment was," she told the Council. "I'm on a boat with folks that have worked their whole lives to protect natural resources. And to feel the gravity of what we were doing was really just truly a heartbreaking thing," she said.