a threat to idaho

In September 2023, ISDA confirmed quagga mussel veligers in the Mid-Snake River, triggering Idaho’s first rapid response plan.

For Idaho, the stakes are enormous. A quagga mussels are incredibly invasive, clogging irrigation systems that farmers depend on, disrupting hydropower facilities that supply affordable energy, and threatening the delivery of water across the state. These impacts would not only drive up costs for irrigators, but also lead to higher utility bills for households. Quagga mussels also create monocultures that would eliminate Idaho’s biological diversity and devastate ecosystems and fish populations. The financial toll of quagga mussels is estimated in the hundreds of millions of dollars of direct and indirect costs.

In 2023, 2024, and 2025, ISDA treated the Snake River’s infested area with chelated copper, all three treatments not only reduced, but contained the quagga mussel infestation. Potholes (ephemeral ponds) outside the river were also treated with potassium chloride (Potash) in early 2025. The 2025 treatment utilized the chelated copper product, Natrix.

August 2026, extensive sampling shows quagga mussel detections in the Snake River once again have decreased from the previous year. Currently, ISDA is detecting 77% fewer veligers than in 2025. As the mussel population in the Mid-Snake River decreases, ISDA has increased diving efforts and even more targeted approaches to earlier detections.

ISDA remains committed to full quagga mussel eradication. The agency will begin a multiphase treatment in the infested area beginning the last week of August, taking action while the infestation remains limited.

2025 Treatment Plan

2026 DRAFT TREATMENT PLAN

A mandatory inspection and decontamination zone from watercraft remains in place along the Snake River from Broken Bridge to Hansen Bridge to prevent the spread. Together, these treatments, monitoring efforts, and containment measures have not only kept the infestation contained but has significantly reduced the impacted area.

Extensive sampling data shows quagga mussel detections have decreased by 77% from 2025. The population remains isolated to the known infested area of the Snake River from just upriver of Twin Falls Dam to Shoshone Falls.
Yes. Extensive sampling following each treatment in 2023, 2024 and 2025 show a decrease in the quagga mussel population in the Snake River, confirming the treatments are working.
2026 sampling has shown a 77% decrease in veliger populations, contained to the known infested area. These results indicate the eradication plan is progressing as intended. As the mussel population in the Mid-Snake River decreases, ISDA has increased diving efforts and even more targeted approaches to earlier detections.
The 2026 treatment plan is being developed by extensive ongoing sampling and careful evaluation of the Snake River’s complex flow patterns and site-specific dynamics.
As in prior years, ISDA will make the treatment plan available to the public prior to implementation. All products and methodologies used will be provided in the public plan.
The Snake River is complex, shifting flows, deep holes, spring inputs and natural refuge areas create challenging conditions that influence treatments. Like any eradication plan in agriculture, these plans take time and strategic effort. While this eradication strategy has shown strong results, it is not a one-time effort but an on-going strategic fight to protect Idaho’s waterways. With more sampling data, a deeper understanding of river dynamics, and a more contained area of the river, ISDA is prepared to effectively treat the quagga mussel population.
Chelated copper treatments in 2023, 2024 and 2025 along with a potassium chloride treatment in 2025, have been the effective at containing the infestation. In addition, ISDA has conducted extensive monitoring of the Snake River and statewide waters and implemented mandatory watercraft inspection and decontamination along the Mid-Snake River.
These efforts have proven to be effective in reducing the quagga mussel population year-over-year. This level of containment is unprecedented among known quagga mussel infestations. Idaho is charting new territory with our eradication effort.
This year, ISDA has conducted over 420 samples in the infested area of the Snake River and more than 3,000 statewide. Sampling in the Mid-Snake river has included veliger and eDNA samples, as well as diving.
View the interactive monitoring map HERE.
ISDA monitors copper levels before, during, and after treatments to ensure safety. The treatment applications are overseen 24/7 by ISDA staff, the contracted applicator, and the product manufacturer. The copper monitoring throughout the treatment occurs at 44 sampling sites in the river throughout the dissipation area.
Idaho Department of Environmental Quality (DEQ) also closely monitors the river for copper levels. This long-term monitoring occurs pre-treatment to set a baseline, during active treatment and continues after treatment to assess impacts.
IDFG conducted pre-treatment fish surveys in both the 2023 and 2024 treatment areas. All sturgeon were marked as hatchery stock, not wild populations. All other fish populations were also accounted for in the pre-treatment fish surveys.
Post-treatment surveys from the 2023 treatment showed expected sturgeon loss, with varying impacts on other species. 2024 post-treatment surveys showed limited fish mortality. Fish populations in the treatment impacted area of the Snake River were not stocked after the 2023 treatment. Observed fish mortality in 2024 was predominately carp and sucker fish. For more information on fish mortality, contact Idaho Department of Fish and Game. https://idfg.idaho.gov/quagga
Quagga mussels disrupt aquatic ecosystems by filtering out plankton, which reduces food availability for fish and other native species. An established quagga mussel population is detrimental to the survival and reproduction of native species, including fish.
Quagga mussels pose a serious threat to Idaho’s infrastructure and ecosystems. They clog pipes that deliver water for drinking, hydropower, agriculture, and recreation. They harm fish populations and wildlife habitat, and dense colonies cause severe damage. A widespread quagga mussel infestation would clog water infrastructure, leading to hundreds of millions of dollars in direct and indirect costs, including higher energy and water bills for everyday Idahoans.
Yes. ISDA is committed to a long-term, science-driven effort to completely eradicate quagga mussels from Idaho waters.
Watercraft inspection and mandatory decontamination are required between Broken Bridge (Yingst Grade) and Hansen Bridge. Any type of conveyance entering the water must be inspected before launch and decontamination after exit at stations at Centennial Waterfront Park, Shoshone Falls, and Twin Falls Reservoir. Access is limited to operating hours at these sites.
Updated information on Snake River access can be found at invasivespecies.idaho.gov/snake-river-access
You are in the right spot! All updates will be posted to this page, Idaho.gov/quagga.