Idaho’s Response
Through ISDA’s Early Detection Monitoring Program, quagga mussels were confirmed in the Twin Falls area of the Snake River on September 18, 2023. The discovery of quagga mussels in the Snake River marked the first time a rapid response plan had been put into action for quagga mussels in Idaho.
The response to the quagga mussel detection in the Snake River is a major priority to the ISDA, Governor Little’s Office, as well as several federal, state and local agencies. The quagga mussel response is an ongoing effort for State of Idaho to protect our waters and way of life from a potentially devastating infestation.
2025 Detection
Sampling data shows a 51% reduction in the quagga mussel impacted area of the Snake River near Twin Falls. Extensive sampling shows the area impacted by quagga mussels is approximately 3.5 river miles, which is down from an impact area of 7.2 miles in 2024. The results show significant progress and demonstrate the effectiveness of ISDA’s ongoing treatment strategy.
No quagga mussels have been detected upriver or downriver of the 2024 treatment zone. Of concern to irrigators in the Magic Valley, no mussels have been detected in nearby reservoirs.
Effectively treating the Snake River presents unique challenges due to the river’s complexity. Freshwater inputs in 2023 and 2024, along with varying river depths and flow rates have influenced how treatments dissipate to the target species. With an inventory of freshwater inputs and a detailed understanding of river dynamics, ISDA has developed a targeted treatment plan for 2025.
ISDA is committed to a strategic, science-driven response to fully eradicate this invasive species and protect the state’s waterways. Similar to 2023 and 2024, ISDA has made its full treatment plan available to the public. The plan will be shaped by extensive ongoing sampling and careful evaluation of the Snake River’s complex flow patterns and site-specific dynamics.
-
Description The 2024 monitoring results showed a decrease of quagga mussel presence in the affected stretch of river since the pre-treatment surveys in 2023. Positive detection locations in September 2024 included in the Shoshone Falls pool, Pillar Falls and the Twin Falls Reservoir behind Twin Falls hydroelectric facility. Quagga mussel reproduction is more active in warmer water temperatures, making late summer the most likely time to detect the mussels in the Snake River.
In response to the 2024 detection, ISDA is implemented a copper treatment in the Mid-Snake River. The treatment took place October 8-20 and utilized the same chelated copper product as the 2023 treatment, Natrix.
In addition to the application of the chelated copper (Natrix), ISDA implemented a potash (potassium chloride) treatment in still water ponds on the Mid-Snake River in February and March. The second treatment reflects the aggressive approach to maximize efforts in the complex river system with the ultimate goal of complete eradication of this species.
Read the 2024 news release HERE.
-
Since the discovery of quagga mussel larvae in the Snake River, ISDA has been dedicated to an aggressive approach for treatment to protect Idaho’s waters from these mussels.
ISDA implemented a treatment of the river with a chelated copper product. It was the first treatment of this type and scale ever attempted in North America. Sampling results indicate the chelated copper treatment was effective in reducing the mussel population.
ISDA utilized a comprehensive treatment strategy, which was developed with the review and assistance of many agencies and groups including; Governor Little’s Office, Idaho Department of Fish and Game, Idaho Office of Species Conservation, Idaho Department of Environmental Quality, Idaho Department of Water Resources, Idaho Department of Parks and Recreation, Idaho Department of Lands, Idaho Power, canal companies, Idaho Water Users Association, U.S. Environmental Protection Agency, U.S. Fish and Wildlife Service, U.S. Geological Survey, U.S. Army Corps of Engineers, U.S. Bureau of Land Management, and U.S. Bureau of Reclamation.
Since the 2023 detection, to today, ISDA has closely coordinated with Twin Falls and Jerome County Commissioners, the City of Twin Falls, and the Idaho Office of Emergency Management.
Containment measures
Today, the Snake River is open with a mandatory decontamination in place from Broken Bridge (Yingst Grade) and Hansen Bridge. Any watercraft or conveyance is required to be inspected prior to launch and decontaminated upon exit of the river. The inspection and decontamination stations are operating at Centennial Waterfront Park, Shoshone Falls, and Twin Falls Reservoir.
Throughout the 2023 and 2024 treatments, ISDA closed public access to the affected stretch of Mid Snake River. The closures were in place to minimize the potential spread of quagga mussels as well as prioritize the public’s safety.
delimiting surveys
To better understand the extent of the physical range of impacted area, ISDA staff survey the water in the Mid-Snake River area for quagga mussel larvae. ISDA staff and partners surveyed at a rapid pace to map out any other presence of quagga mussel larvae or adults in the area.
Samples from the Snake River are sent to a lab to identify any mussel larvae in the samples through microscopy. Any samples identified as possible quagga mussel are then transferred to another lab for PCR (genetic) confirmation.
Sampling occurs statewide as well as in surrounding lakes and reservoirs, upstream from Milner Dam to American Falls, and downstream to the Idaho Power Dam Complex at Hagerman.
No mussels have been detected in nearby waterbodies.
Treatment Notifications
The ISDA along with several partners work to inform residents of the Magic Valley and all Idahoans of the quagga mussel response efforts. Communication to the public is a crucial aspect of the rapid response plan. The following communication methods were employed.