Idaho reports 77% reduction in quagga mussels in Snake River

The Idaho State Department of Agriculture is detecting 77% fewer quagga mussel veligers, the larval stage, in the Snake River than it did in 2025, the agency announced Monday, marking another year-over-year decline in the invasive species population.

ISDA has conducted more than 420 samples in the infested stretch of the Snake River this year and more than 3,000 statewide. As detections have fallen, the agency has expanded diving efforts and shifted to more targeted early-detection methods.

The agency plans to begin a multiphase treatment in the infested area during the last week of August.

“Our previous treatments have proven to be effective, and this level of containment is unprecedented among known quagga mussel infestations,” said ISDA Director Chanel Tewalt. “No other state has a proven playbook for how to accomplish this work. Idaho is charting new territory with our eradication effort.”

Gov. Brad Little credited the state’s aggressive response for the results, warning that delay carries long-term costs.

“Those delayed responses have resulted in significant long-term management costs coming directly out of taxpayer pockets,” Little said. “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.”

ISDA pointed to California‘s experience with golden mussels as a cautionary example. Golden mussels — similar in destructiveness to quagga mussels — were detected near Sacramento in October 2024. Without a full eradication program, the species has since spread nearly 500 miles, from the Sacramento area to San Diego. One California irrigation provider spent nearly $3 million on cleanup earlier this year, and the Water Association of Kern County estimates $9 million in cleanup costs alone.

In Idaho, inaction could cost downstream water users an estimated $69 million annually in treatment costs alone. More than 1,700 users draw Snake River water between Twin Falls and Lewiston, including irrigation providers, hydroelectric facilities and municipal drinking water systems.

Quagga mussels clog irrigation infrastructure, disrupt hydropower operations and threaten water delivery across the state. ISDA said it will release its treatment plan publicly before implementation begins.

This story was written using artificial intelligence with human oversight.