ISDA details 2024 mid‑Snake quagga mussel response: expanded sampling, targeted copper treatment

The Idaho State Department of Agriculture (ISDA) briefed the House Agriculture Affairs Committee on the agency’s 2024 response to quagga mussel detections on the mid‑Snake River, describing expanded inspections, enhanced laboratory confirmation and a complex chemical treatment intended to suppress a small but unacceptable reproductive population.

“Thanks to folks like Representative Miller and many others, we have increased by every single measure what we do in this program,” ISDA Director Chanel Tewalt told the committee as she summarized 2024 activity. The department described a stepped‑up approach: more boat inspections (about 50% more than the prior year), doubled statewide water sampling, added laboratory partners and the use of environmental DNA (eDNA) as one tool among several for delimiting the detection area.

Why it matters: Quagga and zebra mussels attach to hard surfaces, can reproduce prolifically, and pose known risks to irrigation infrastructure, hydropower facilities and municipal intakes. Idaho’s water and energy systems rely on clean infrastructure; the department said federal and state partners were focused on preventing an established population.

Detection, delimiting and confirmation ISDA reported a limited detection of quagga mussel veligers on Sept. 24, 2024. The department stressed its laboratory confirmation process is multi‑step: visual assessments, double‑blind review by outside taxonomic experts, molecular confirmation and cautious use of eDNA to avoid false positives. Bureau Chief Nick Zerflue described the agency’s field protocol: “We’re going to start brand new, fresh, clean plankton nets, paying really close attention to how we’re sampling, the order in which that we’re sampling, the cleanliness of our gear,” and added that samples are being doubled up and analyzed by multiple labs to ensure quality control.

Treatment and operational approach ISDA described a targeted chemical treatment on the mid‑Snake performed in October 2024. The plan, developed with applicators and the product manufacturer, used a chelated copper product applied to maintain approximately 1 part per million in the treatment polygons and extended contact time to a 200‑hour treatment window once the target concentration was achieved. The agency reported that treatment began Oct. 8 and concluded Oct. 19, and that “just over 60,000 gallons of product was deployed,” a figure cited by agency staff. ISDA emphasized the treatment was executed under label authority and with consultation from the product manufacturer, SePRO, and other technical partners.

Partners, access and logistics ISDA credited a wide array of partners: contracted applicators, the product manufacturer, multiple diagnostic labs, the University of Idaho, Idaho Power (for access and flow augmentation within hydroelectric facilities), county and city cooperators in Twin Falls and Jerome counties, and emergency and resource agencies for aerial and boat support. The department said that operational challenges included deep pools, springs, isolated ponds, access within hydroelectric facilities, and the need to calibrate flows to achieve and maintain the treatment concentration. Simplot’s Twin Falls distribution operations were cited as a logistical partner for product delivery.

Monitoring and current status Agency staff said the number of veligers detected in 2024 was smaller than in 2023 and that no adult mussels were observed during 2024 scuba and visual surveys, a fact the department described as encouraging but not conclusive. Zerflue said the population appears very small—the type of scenario where eradication efforts have a reasonable chance of success—but that any detection remains unacceptable to state officials.

Questions and enforcement considerations Legislators asked whether ISDA has sufficient funding and staffing going forward and how to reduce the risk of re‑introduction from out‑of‑state boat traffic. Tewalt said the program is well resourced and has legal authority under Idaho law enacted in 2008, but noted practical enforcement of out‑of‑state boater requirements relies on local law enforcement cooperation. The agency recommended continued statewide sampling, boat inspections and interagency partnerships.

ISDA closed by urging continued vigilance, expanded partnerships and public communication to reduce the risk that infested boats or gear transport mussels between water bodies.