Idaho agriculture department details extended quagga mussel sampling and October 2024 treatment on Mid‑Snake River

Chanel Tewalt, director of the Idaho State Department of Agriculture, and Nick Zerflue, ISDA bureau chief overseeing invasive species response, told the House Agriculture Affairs Committee on Feb. 14 that the department increased inspections, expanded water sampling and carried out a large‑scale treatment on the Mid‑Snake River after quagga mussels were detected in 2023 and again at low levels in 2024.

Tewalt said Idaho’s 2008 Invasive Species Act called on the department to set up boat‑inspection stations and to run the state program. She told lawmakers the department inspected about 50% more boats statewide in 2024 than in 2023 and “doubled water sampling in every single one of your districts.” The department also launched a communication campaign and broadened laboratory support and subject‑matter expertise used to confirm detections.

ISDA said it uses a layered verification process. After an initial visual or plankton‑net detection of veligers the agency seeks genetic confirmation, cross‑checks images and samples with multiple specialist laboratories and uses carefully applied environmental DNA (eDNA) sampling as part of the diagnostic toolkit. “EDNA can be used imprecisely. It can cause panic when folks don't use it judiciously,” Tewalt said, and ISDA staff described collaborating with University of Idaho and Pisces laboratories for eDNA analysis.

The department said it first found quagga veligers in the Snake River in 2023 and performed the first large‑scale, targeted treatment that year. In 2024 ISDA continued intensive sampling and delimitation; the agency reported fewer veligers in 2024 than in 2023 but said any detection is unacceptable. The agency identified a small number of veligers in the Sageview area upriver of Twin Falls Dam — a location the department characterized as a logical launching point for larger vessels and ballast‑water vectors — and moved quickly to design and deploy a treatment plan that covered Twin Falls Reservoir and about 8.6 river miles.

Zerflue described the sampling and treatment logistics: fresh plankton nets and strict decontamination procedures in the field, redundant laboratory checks and cross‑jurisdictional coordination. ISDA contracted with private applicators and worked with SePRO (the chelated copper manufacturer) and local distributors to secure product. The department applied a chelated‑copper product calibrated to maintain about 1 part per million concentration and extended the contact time to a 200‑hour treatment window; the 200‑hour clock began only after ISDA confirmed the target concentration in field measurements. The October 2024 operation deployed about 60,000 gallons of product via applicator boats and strategically placed metering totes and included flow coordination with Idaho Power and stream‑gage support from the Idaho Department of Water Resources.

ISDA officials emphasized the operational challenges: a complex river system with deep pools, springs and upwellings; access inside hydroelectric facilities; and the need to protect downstream sensitive species (notably two listed Snake River snails). ISDA said it prepared contingency measures — activated charcoal and other removal approaches — but did not need to deploy the contingency plan to remove copper downstream.

Tewalt and Zerflue credited a broad partnership that included county and city officials, federal agencies, Idaho Power, contracted applicators and multiple lab partners, and they thanked many staff and volunteers for extended field work. On enforcement and prevention, Tewalt said Idaho law prohibits hauling boats with ballast water into state waters and requires inspections for out‑of‑state boats but that ISDA has limited direct enforcement authority; she urged better cooperation with local law enforcement and greater public awareness to reduce human‑mediated spread.

Ending: ISDA told the committee it will continue intensified year‑round inspections, expanded sampling and multi‑laboratory confirmation; agency leaders said they stand ready to respond quickly to any future detections but cautioned that sustained prevention will require continued funding, partnerships and public cooperation.