Snake River Quagga Mussel
September 2023 - The ISDA confirmed the presence of quagga mussel in the Mid-Snake River. These findings marked the first time a rapid response plan had been put into action for quagga mussels in Idaho.
Closures are in place along the Snake River until further notice. See map below for closures and mandatory decontamination zone.
Closures are in place in and along the Snake River until further notice. The public’s cooperation in staying out of the impacted area is crucial to the success of our efforts. Temporarily closing waterbodies is critical to responding to the situation and to minimizing any potential movement of quagga mussels.
Under temporary rule (IDAPA 02.06.09) ISDA has closed public access to the river from Twin Falls Hydroelectric Dam to Pillar Falls.
Public access 6a.m. to 10p.m. from Pillar Falls to Yingst Grade (known as “the Broken Bridge,” “Yingst Grade Bridge,” or “the Old Interstate Bridge”) is open. Decontamination for watercraft entering and exiting the river between Yingst Grade and Pillar Falls is mandatory. See "Hot Wash Decontamination" below for more information.
This is a dynamic situation, please see the latest closure map below.
Any watercraft or conveyance is required to be decontaminated prior to launch and upon exit of the river.
Watercraft includes but is not limited to boats, kayaks, paddleboards and other devices used in water. Conveyances including duck decoys, waders, fishing tackle, life jackets, and anything that has touched the water must also be decontaminated. ISDA watercraft inspections and decontaminations are free to the public.
Centennial Waterfront Park
Canyon Springs Rd
Twin Falls, ID 83301
6a.m. to 10p.m. *weather dependent
Call 1-877-336-8676 for more information.
The introduction of quagga mussels poses a major threat to Idaho. This invasive species can quickly spread and clog pipes that deliver water for drinking, energy, agriculture, recreation, and a variety of other uses. These mussels can negatively affect fish populations and wildlife habitat.
The mussels are highly competitive, persistent, and can create monocultures that will eliminate Idaho's diverse biological landscape.
A quagga mussel infestation has the potential to cost Idaho hundreds of millions of dollars in actual and indirect costs. It could prompt increases in your taxes and bills.
Your cooperation is essential to ISDA's efforts against aquatic invasive species. See how you can help below.
CLEAN, DRAIN, DRY ALL WATERCRAFT AND ITEMS THAT GO IN THE WATER – This situation is reminder to anyone who has watercraft or items you put in the water to be vigilant in practicing the steps of CLEAN, DRAIN, DRY before putting your watercraft or item back in the water. This includes boats, kayaks, paddleboards, canoes, oars, waders, boots, lifejackets, fishing gear, buckets, nets, and other items.
Decontamination - Decontamination for watercraft entering and exiting the river between Broken Bridge (Yingst Grade) and Pillar Falls is mandatory. This applies to all watercraft launches anywhere in this defined area. Watercraft launched at any access points between Broken Bridge (Yingst Grade) and Pillar Falls (i.e. Auger Falls Park and Jerome County north shoreline access) must be decontaminated at Centennial Park. DO NOT attempt to decontaminate watercraft yourself. Call 1-844-311-4873 for hot wash information.
Stay out - Closures are in place in and along the Snake River until further notice as the investigation in the area continues. The public’s cooperation in staying out of the impacted area is crucial to the success of ISDA’s efforts.
ISDA implemented a rapid response plan that included notifying impacted entities, implementing containment measures, conducting delimiting surveys and evaluating for potential treatment options.
Containment Measures:
ISDA has closed off public access to the Snake River between Twin Falls Hydroelectric Dam and Pillar Falls. Public access closure includes, but is not limited to prohibiting any persons, watercraft, pets, decoys, and fishing tackle from accessing the water. Accessing the water in the ISDA closed area of the Snake River is a violation of Idaho Code (IDAPA 02.06.09).
This is a dynamic situation – please see the map below for the latest information on closures.
Delimiting Surveys:
To better understand the extent of the physical range of impacted area, ISDA staff surveyed the water in the Mid-Snake River area for quagga mussel larvae. Samples from the Snake River were then sent to a lab to identify any mussel larvae in the samples. Before the treatment, sample results indicated a population of quagga mussel larvae specifically in the Shoshone Falls area. The survey data was used in ISDA’s treatment planning.
Control Strategy:
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. The ten day treatment began October 3 and concluded October 13, using a comprehensive treatment plan. The copper-based treatment (Natrix) was applied at a rate that will eradicate mussels but is below the drinking water standard for humans. The treatment application occurred across a sixteen-mile section – less than one percent – of the Snake River and is intended to eradicate quagga mussels at all life stages. Click "Quagga Mussel Treatment" above for more treatment information.
Post-Treatment:
Copper levels in the Snake River dissipated as anticipated and ISDA is not detecting any additional copper in the river system.
The adult mussel that was identified in the river pre-treatment experienced mortality within 48 hours of the first treatment block. Although initial veliger sample results indicated the treatment impacted larvae and adult populations, it is premature to conclude complete eradication at this stage. Quagga mussels generally stop reproducing once the water is below 14 degrees Celsius. Sampling will begin again in the spring once water temperatures reach 14 degrees Celsius. Surveying will be an ongoing effort to determine the success of the treatment.
Quagga mussels have emerged alongside Zebra mussels as one of the most aggressive invasive species infesting the United States. These mussels spread easily to new areas due to the movement of watercraft. Learn more about quagga mussels at invasivespecies.idaho.gov.
A veliger is the free-swimming larval stage of a quagga mussel. Quagga mussel veligers are quagga mussels at larval life stages. Veligers are microscopic and cannot be seen with the naked eye.
For the past 15 years, the ISDA has been conducting routine samples in waterbodies to monitor for potential aquatic invasive species across the state. Outside of the recent Snake River findings, ISDA has not found live quagga mussel larvae in any other Idaho waterbody. The program works to detect new outbreaks early, which allows ISDA to act quickly to control populations.
Click the map below to view interactive map.
The Snake River public access closure is from Pillar Falls to the Twin Falls Hydroelectric Dam.
Mandatory decontamination applies to any watercraft prior to launch and upon exiting the river between Broken Bridge (Yingst Grade) and Pillar Falls. Click on map to view mandatory decontamination zone.
