Idaho agriculture department details quagga mussel detections and large-scale treatments on Mid‑Snake River

Chanel Tewaltz, director of the Idaho State Department of Agriculture, briefed the Senate Agriculture Committee on quagga mussel monitoring and the department’s 2023–24 rapid responses on the Mid‑Snake River. "The Invasive Species Act was passed in 02/2008 by the Idaho legislature unanimously," she said, describing the agency’s statutory duty to operate boat inspections and response efforts.

Tewaltz and Nick Zirflo, bureau chief for the department’s invasive‑species program, described an expanded monitoring effort in 2024, including a statewide doubling of sampling and a 50% increase in watercraft inspections. Zirflo said the department uses a mix of sampling methods — plankton tow nets for veligers, targeted adult sampling, molecular confirmation and carefully applied environmental DNA (eDNA) — and that eDNA hits require follow-up because dead tissue can yield DNA even after mussels are nonviable.

Following small detections of veligers in the Mid‑Snake, the department organized an accelerated, multi‑agency response and implemented a large aquatic treatment in October 2024. "We started on October 8... the treatment concluded on October 19; roughly 63,000 gallons of Matrix was applied," Zirflo said, referring to the chelated‑copper product manufactured by SePRO. The treatment plan maintained a target concentration of about 1 part per million and an operational window of about 200 hours once the treatment reached the target concentration.

Officials described logistical challenges: complex river bathymetry and flow, deep pools and isolated ponds, coordination with Idaho Power and FERC to maintain steady flows, specialized applicator boats and helicopter placement of gear in inaccessible pools. The department said copper levels returned to baseline around Nov. 8 and emphasized that long‑term effectiveness will require follow‑up sampling in the next warm season. Zirflo said the agency expects to resume sampling in May–June when water temperatures allow spawning detection and spring flows permit safe access.

Department leaders said Idaho’s response has involved state, federal and private partners, that the state expanded lab redundancy for molecular confirmations, and that they intend to balance robust monitoring and treatments with community access and economic concerns for Twin Falls and Jerome counties. Director Tewaltz told the committee the department’s approach pairs data and science with local context and transparency.