ISDA describes 2024 Snake River response, expanded sampling and a 200‑hour chelated‑copper treatment

Chanel Tewalt, director of the Idaho State Department of Agriculture, and Nick Zerflue, the ISDA bureau chief who oversees the invasive species response, updated the House Agriculture Affairs Committee on the agency’s 2024 activities to detect and respond to quagga mussel veligers in the Snake River.

Tewalt outlined the program expansion: ISDA inspected about 50 percent more boats in 2024 than in 2023 and doubled water sampling statewide. She said sampling is now published and available so “it'll tell you who pulled the sample, where they were, when they pulled the sample and what we found in that location.”

ISDA reported a delimiting detection of quagga mussel veligers in the mid‑Snake in late September 2024. After molecular confirmation, agency teams undertook targeted delimit sampling to identify the leading edge of the detection and then planned a treatment. Zerflue said the population detected in 2024 was smaller than in 2023: “we have a reduced population and producing fewer veligers than what was observed in 2023.” He added that field teams did not observe any adult mussels in 2024.

Treatment and partners: ISDA described a multi‑partner operation in October 2024 that targeted Twin Falls Reservoir and about 8.6 river miles of the Snake. The agency applied matrix/chelated copper to reach and maintain about 1 part per million (ppm) and extended engineered contact time to 200 hours, a longer duration than the 2023 effort. Tewalt and Zerflue said ISDA coordinated with SePRO (the copper manufacturer), a contracted applicator (Clean Links), Simplot as a local distributor, Idaho Power (for access and flow management within hydro facilities), Idaho Department of Water Resources (for flow measurement), University of Idaho and Pisces laboratory partners for eDNA and confirmatory testing, US Fish and Wildlife Service and EPA for consultation, and local responders.

Zerflue provided operational details: treatment started October 8 and concluded October 19, 2024; the agency deployed roughly 60,000 gallons of chelated copper via 275‑gallon totes and applicator boats and metering systems; flow augmentation and careful calibration were used to obtain consistent downstream mixing. ISDA described logistics that included helicopter sling‑loads to access remote pools and on‑site breakfasts to coordinate daily tasks; the agency said it stood up a multi‑lab diagnostic process to avoid false positives from lab cross‑contamination and used double‑blind image reviews and molecular confirmation before public notifications.

Why it matters: ISDA said the Snake River detection is the first time quagga mussel veligers were found in the Columbia River basin, making the response regionally significant. Tewalt emphasized the limits of enforcement for out‑of‑state boaters and said the state must rely on partnerships with law enforcement and local communities to manage introduction risk.

Committee questions and resources: Representatives asked whether ISDA has the resources to maintain expanded inspections and sampling; Tewalt said the program is “well resourced” and highlighted the need for continued local cooperation and law enforcement support at key entry points. Representatives also asked about public cooperation at inspection stations; Tewalt said most boaters who stop are cooperative and that noncompliance is usually inadvertent rather than malicious.

Ending: ISDA asked legislators to maintain support and partnerships as the agency continues sampling, inspection and targeted responses in 2025; no committee policy votes were taken on these operational activities during the hearing.