08/18/2026
UPDATE ON QUAGGA MUSSELL
Boise, Idaho — The Idaho State Department of Agriculture (ISDA) announced today that 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.
“Other states have shown us what happens when invasive mussel infestations are allowed to establish before action is taken,” said Governor Brad Little. “Those delayed responses have resulted in significant long-term management costs coming directly out of taxpayer pockets. Idaho has set the standard by responding aggressively. Our responsible strategy on the Snake River is proving to be effective, and we will continue making decisions that give us the best opportunity to eliminate quagga mussels to protect Idaho’s waters and the people who depend on them.”
“We know what is at stake if invasive mussels gain a foothold in Idaho,” said ISDA Director Chanel Tewalt. “Our previous treatments have proven to be effective, and this level of containment is unprecedented among known quagga mussel infestations. No other state has a proven playbook for how to accomplish this work. Idaho is charting new territory with our eradication effort.”
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.
Lessons from California Golden Mussel Infestation
In October 2024, golden mussels, which are similar in destructiveness and proliferation to quagga mussels, were detected in the Port of Stockton near Sacramento. California was not able to initiate a full eradication program due to limiting factors. Today, golden mussel veligers can be found from the Sacramento area to San Diego, which is nearly 500 miles away. The Snake River from Twin Falls to the confluence with the Clearwater River near Lewiston is a similar distance. In under two years, the unmitigated spread of invasive mussels could be extensive.
Additional maintenance costs are already being seen among California water users. Earlier this year, one California irrigation provider spent nearly $3 million on cleanup efforts using a copper-based product to remove golden mussels. The Water Association of Kern County, California estimates $9 million in cleanup costs alone.
The Cost of Inaction
Inaction in Idaho would create a need for annual treatments of irrigation systems, hydroelectric facilities and other water systems, which could cost downstream users $69 million each year for treatment product alone. More than 1,700 users rely on Snake River water from Twin Falls to Lewiston, ranging from small water users and irrigation providers to municipal drinking water systems. The treatments for all downstream water intakes would include thousands of pounds of chemical products intended to kill mussels. The treatment costs would ultimately be passed on to Idahoans.
In 2026, ISDA has conducted over 420 samples in the infested area of the Snake River and more than 3,000 statewide.
As in prior years, ISDA will make the treatment plan available to the public prior to implementation. The treatment plan is informed by extensive ongoing sampling and careful evaluation of the Snake River’s complex flow patterns and site-specific dynamics. All products and methodologies used will be provided in the public plan.
ISDA will work with local jurisdictions and property owners regarding river access for treatment.
Quagga mussels are highly invasive, clogging irrigation systems that farmers depend on, disrupting hydropower facilities that supply affordable energy, and threatening the delivery of water across the state.
