State agriculture officials describe expanded quagga mussel surveillance and large-scale 2024 treatment on the Mid‑Snake River

Department of Agriculture officials told the Senate Agriculture Committee the state has expanded invasive‑species surveillance and undertook an extensive 2024 response after limited detections of quagga mussel veligers on the Mid‑Snake River.

Chanel Tewall, director of the Idaho State Department of Agriculture (ISDA), told the committee that the 2008 Invasive Species Act directs the agency to maintain boat check stations and a response program. ISDA Director Tewall and bureau chief Nick (last name provided in transcript) described program changes since the committee last reviewed the issue: ISDA doubled statewide sampling, increased watercraft inspections by about 50%, added more sampling stations and lab partners, and expanded public communication to target out‑of‑state visitors.

ISDA said it found only very small numbers of veligers (the free‑swimming juvenile stage used to detect mussels), including isolated detections upstream of Twin Falls Dam in 2024. Officials stressed that detection is typically by veliger sampling rather than finding adults and that eDNA (environmental DNA) can indicate presence of genetic material even when organisms are not viable, so ISDA uses molecular confirmation and multiple laboratory reviews to avoid false positives.

ISDA described a large chemical treatment in October 2024 carried out after rapid planning. The agency said it deployed a 200‑hour treatment objective using a chelated‑copper product (Natrix, manufactured by SePRO) at a target concentration of 1 part per million. The treatment began Oct. 8 and concluded Oct. 19; ISDA reported roughly 63,000 gallons of product were applied in an operation it described as about 40% larger than the 2023 effort and the largest of its kind attempted in North America. ISDA said it delayed the treatment clock for several days to ensure adequate mixing and to confirm a maintained 1 ppm concentration before counting treatment hours.

ISDA officials detailed operational challenges: complex hydrology, deep pools and isolated ponds, the need for access agreements with multiple landowners and Idaho Power, and monitoring for downstream copper concentrations and impacts to sensitive species. ISDA said it worked with federal and state partners, the University of Idaho Hagerman Center, an international contractor experienced in aquatic treatments, and a local distributor (Simplot) to move product and logistics. Officials said they will resume sampling in the warmer months (May–June timeframe) to assess whether the 2024 treatment reduced veliger detections.

Committee members asked about timelines and comparisons to other states. ISDA staff described Montana’s Canyon Ferry case as an example where early detections were managed through containment and monitoring; Canyon Ferry was later removed from an infested list after five years of monitoring with no further detections. ISDA officials urged transparency, lab redundancy, and community engagement and said the agency aims to avoid recurring fall treatments through aggressive early action and broad surveillance.

ISDA emphasized there are tradeoffs between keeping public access and implementing intensive response actions. Officials said Twin Falls and Jerome counties bore the brunt of the 2024 operations and that the agency worked to limit closures where possible while continuing monitoring.