The Idaho State Department of Agriculture on Oct. 8 will start a 10-day chemical application that aims eradicate invasive quagga mussels on part of the Middle Snake River near Twin Falls.

ISDA on Sept. 24 confirmed that its investigators found a small number of the invasive mussels in several water samples. Officials did not further quantify the finding, which came about a year after larvae and a live adult quagga were found in the same area during routine monitoring.

Quagga and zebra mussels can cause major damage to irrigation and drinking water infrastructure as well as hydropower equipment.

The tiny mussels can attach to watercraft and equipment transported between water bodies.

Following the 2023 quagga finding, ISDA and partner organizations used copper-based Natrix, which reduced the population significantly, according to the department.

U.S. Environmental Protection Agency-approved Natrix is applied at one part per million, which is below drinking water standards.

The department and contractors plan to apply Natrix in an eight-mile stretch from downstream of Hansen Bridge to Centennial Waterfront Park. River access from Hansen Bridge to Yingst Grade is closed.

Officials recommend that people stay out of the 18-mile dissipation area downstream from Hansen Bridge to Kanaka Rapid, according to the release.

ISDA and the state Department of Environmental Quality will routinely monitor treatment effectiveness and copper dissipation.

The department is working with Idaho Power Co. and canal company representatives to take advantage of dropping Snake River flows, ISDA public information officer Sydney Kennedy told Capital Press.

Another treatment, to target quagga mussels in stillwater and deep pool sections, is planned in November.

The treatment plan reflects “Idaho’s commitment to using every available tool to combat this threat,” ISDA director Chanel Tewalt said in the release. “By combining targeted treatments with ongoing monitoring, we are maximizing our efforts with the ultimate goal of eradication.”