Persistent Invasive Species Challenge Twin Falls County Waters
Quagga mussels have been detected in the Snake River near Twin Falls for the fourth consecutive year, prompting state water management officials to refine their chemical treatment approach this week. The most recent sampling found eight larval veligers and seven adult mussels in the river system, officials confirmed.
The Idaho State Department of Agriculture, which oversees the state’s response to the invasive species threat, reported that treatment efforts over the past year achieved a 77% reduction in both adult quagga mussels and larval veligers. That progress has eliminated what had become a focal point of concern: a concentrated population plume located below Shoshone Falls, which officials had identified as a troublesome hotspot.
Chanel Tewalt, director of the Idaho State Department of Agriculture, acknowledged the mixed results. “We have definitely seen a reduction of the population, so that’s not in dispute. We’ve gone from having a plume below Shoshone Falls — a hotspot, if you will — that hotspot is gone,” Tewalt told KIVI-TV.
New Chemical Strategy Targets Deeper Water Zones
The upcoming treatment plan represents a scaled-back effort compared to previous years’ operations. Rather than covering the broader stretches of river that received treatment before, the new approach will concentrate on two specific zones: the waters above Shoshone Falls and the area above Twin Falls Dam.
The revised strategy incorporates two chemical compounds to address different parts of the riverbed. Chelated copper will serve as the primary treatment agent, while sulfurized copper will be added to penetrate the rocky terrain between 20 and 40 feet below the surface — a depth range where the harder substrate requires more aggressive chemical penetration to reach mussel populations.
The timing of this year’s mussel detection also represents a departure from past patterns. Officials noted that quagga mussels appeared in the system earlier than they had in the three previous years of confirmed sightings, adding another variable to management planning.
Uncharted Territory in Mussel Management
State water officials have emphasized that Idaho’s effort to chemically treat an infested river system without relying on complete drawdown or physical barriers represents pioneering work in invasive species management. “There’s no proven example of this occurring anywhere else in the US to our knowledge, so it’s not as if we have a metric by which to compare our project,” Tewalt told KIVI-TV.
Quagga mussels pose a significant threat to irrigation infrastructure, hydroelectric operations, and water delivery systems throughout the Snake River basin. The mussels attach to pipes, screens, and intake structures, reducing water flow and requiring costly removal and maintenance. Their presence in the Snake River system has elevated the stakes for water management agencies across the region.
The four-year persistence of quagga mussels in Twin Falls County waters underscores the difficulty of eliminating invasive aquatic species once they establish a foothold. The species likely entered the Snake River system through ballast water in boats or other vectors from reservoirs in the western United States where quagga mussels have proliferated since the 1990s.
Idaho’s water infrastructure faces mounting pressures from aging systems and competing demands. State officials have worked to secure funding and coordinate treatment efforts across multiple agencies and water users who depend on the Snake River.
What Comes Next
The Idaho State Department of Agriculture is expected to roll out the new treatment plan this week, focusing operations on the two priority zones identified along the Snake River. Monitoring will continue to track mussel populations and assess the effectiveness of the revised chemical strategy. State officials have indicated that ongoing detection and treatment efforts will likely continue for the foreseeable future as long as quagga mussels remain present in the system.
For irrigation districts, municipal water providers, and other water users in Twin Falls County and downstream, the persistent threat means continued vigilance and potential disruptions to normal operations during treatment periods. The state has urged water users to maintain screening and intake monitoring protocols to prevent mussel colonization of local infrastructure.