Idaho Department of Agriculture outlines expanded response after quagga mussel detections in the Mid‑Snake

Chanel Tewall, director of the Idaho State Department of Agriculture, and Nick (bureau chief, Invasive Species Program) described expanded monitoring and a large response after limited quagga mussel detections in the Mid‑Snake River.

Tewall told the Senate Agriculture Committee that the Idaho Invasive Species Act (passed in 2008) requires the agency to maintain boat check stations and a response program. She said the department doubled sampling statewide and increased watercraft inspections by roughly 50 percent since last year. “We fulfilled that promise,” Tewall said, referring to a commitment to increase monitoring statewide.

The department summarized 2023 and 2024 actions. In 2023 the agency carried out what it described as the largest treatment of its kind attempted in North America. In 2024 the team expanded the treatment area and lengthened the operational exposure: the department said it applied roughly 63,000 gallons of a chelated‑copper molluscicide (Matrix/Natrix, manufactured by SePRO) over a 200‑hour treatment block and started treatment October 8; the treatment concluded on October 19. The 2024 operation was about 40 percent larger than the 2023 treatment, the presenters said.

Staff described a three‑pronged approach: agency field crews (sampling, delimiting surveys, inspections), the product manufacturer advising on chemistry and concentration, and a contractor experienced in aquatic treatments. The treatment plan aimed to reach and maintain approximately 1 part per million copper concentration across the treatment area and to sustain that concentration for 200 hours, a longer exposure than used previously. The department said it worked with multiple state and federal agencies, hydropower operators and local stakeholders to manage flows and check water‑quality and species impacts during and after the application.

The presenters explained detection methods. The agency uses tow‑net sampling for veligers, adult sampling where practical, blinded laboratory confirmations, multi‑lab molecular (DNA) confirmation, and strategic use of environmental DNA (eDNA) testing while noting eDNA can indicate the presence of genetic material without confirming live, reproducing mussels. They cautioned that veliger detections are seasonal—occurring primarily during late summer and early fall warm periods—and that program staff must wait for appropriate water temperatures to assess treatment effectiveness. Nick told the committee the agency expects to resume sampling in May–June when water temperatures generally rise.

Committee members asked about coordination with other states, lessons from Montana water bodies that were later removed from infested lists, and the balance between response and community impacts. Tewall said the agency sought to be transparent about the treatment, including potential fish mortality, and to combine science with community considerations when reopening access to recreation. Several senators thanked the presenters for the state response and for bringing stakeholders and federal partners into the effort.

The department made data and monitoring maps public on its website and urged constituents to consult those resources for site‑level sampling data.