Idaho’s aggressive effort to eliminate quagga mussels from the Snake River is moving into a new phase, with the State Department of Agriculture deploying divers and chemical treatments to two strategically important reservoir pools as the invasive species shows a dramatic decline.
The expanded 2026 campaign comes after state officials quashed rumors circulating through Twin Falls County about a resurgence of the mussel population. Agriculture Director Chanel Tewalt clarified that the presence of 10 divers in a stretch of the Snake River earlier this month was part of a planned mapping and injection operation—not a response to a new infestation.
“No other state has a proven playbook for how to accomplish this work,” Tewalt told officials overseeing the eradication effort. “Idaho is charting new territory with our eradication effort.”, as first reported by the Times-News
Twin Falls County Commissioner Brent Reinke said community concerns about the divers likely stemmed from the visible presence of workers in the river. The diving operations, conducted over several days, were designed to assess conditions in key areas and prepare for the next stage of treatment, according to the Idaho State Department of Agriculture.
Historic Decline in Mussel Population
The quagga mussel infestation, first detected in Idaho waters in 2023, has contracted dramatically. As of mid-August, the agriculture department reported a 99 percent decline in mussel presence compared to 2024 numbers—a sign that earlier eradication efforts have yielded significant results.
The 2023 campaign to combat the initial outbreak was sweeping in scope, involving helicopters, boats, and fine drag nets deployed across the entire Snake River. That intensive effort appears to have succeeded in reducing the population to manageable levels, though complete elimination remains the state’s goal.
Two Deep Pools Targeted for Treatment
The agriculture department has identified two deep pools as priority sites for the upcoming treatment: one above Shoshone Falls and another above Twin Falls Dam. These areas have proven to be refuges for the remaining mussel population because of the rocky terrain, natural fissures, and freshwater inflow that provide cover and suitable conditions for the organisms to survive.
The new treatment strategy relies on divers working in combination with mollusicide applications—chemical compounds designed to kill mollusks. The department plans to deploy three separate sets of mollusicide treatments at safe harbors within the two pools, targeting locations where mussels are most likely to congregate.
The approach reflects lessons learned from the 2023 eradication campaign and represents an evolution in Idaho’s response to the invasive species. Rather than the river-wide mobilization required in 2023, this year’s effort focuses resources on the specific deep-water refuges where the remaining population has concentrated.
What Comes Next
The agriculture department released details of the treatment plan on Monday, signaling that the diving and chemical injection operations will proceed in coming weeks. State officials have emphasized the importance of the diver teams in accurately mapping mussel locations and ensuring that mollusicide treatments reach the isolated pools where the species has retreated.
Success in eliminating the quagga mussel would protect Idaho’s waterways and the broader region. The species poses a threat to irrigation infrastructure, hydroelectric facilities, and recreational water systems across the western United States. Idaho’s aggressive eradication strategy—now two growing seasons in—has positioned the state as a leader in invasive species control, even as officials acknowledge they are navigating uncharted territory.
Continued monitoring and treatment of the Snake River will remain essential through the remainder of the season. State wildlife managers expect to provide updates as the 2026 treatment campaign progresses.