On September 18, 2023, the presence of quagga mussels was confirmed in the Snake River near Twin Falls during routine invasive species monitoring by the Idaho State Department of Agriculture (ISDA). The discovery of this invasive, non-native species is very troubling and the potential spread to the entire Snake and Columbia River systems would be catastrophic, with the potential to significantly disrupt aquatic ecosystems and trigger widespread economic impacts.

Quagga distribution in the Snake detected September 2023. ISDA photo.

What’s the deal with quagga mussels?

Quagga mussels were first detected in the U.S. in the Great Lakes in the 1980s, and are believed to have been introduced from the ballast of ships traveling from Eastern Europe, the mussels are native to Ukraine and Russia. Quaggas have since spread across much of the U.S., resulting in significant ecological and infrastructure impacts with high economic costs.  

Up until last month, the Columbia River Basin, which includes the Snake River, was the last major river system in the U.S. that remained free of this invasive pest.

Invasive mussels have spread across every major river system in the continental U.S. with one exception, the Columbia River Basin. USGS Map.

Quagga mussels are filter feeders and can outcompete fish and other aquatic species, and in the Great Lakes, Lake Powell, Lake Mead, and other infested areas, have disrupted entire ecosystems. Mussels can target specific species of plankton, which can lead to increases in outbreaks of toxic algae, which are a consistent problem in downstream Snake River reservoirs. The invasive pests can also outcompete native mollusks and can foul boats, buoys, docks, pipes, hydropower, irrigation, and other infrastructure. Conservative estimates indicate that invasive mussels could cost the state over $100 million per year.

What is the plan to control this pest?

In response to the recent detection of quagga larvae (known as veligers) and at least one adult mussel, ISDA has coordinated a rapid response in coordination with other state and federal agencies including Idaho Department of Fish and Game, Idaho Department of Environmental Quality, U.S. Fish and Wildlife Service, Environmental Protection Agency, Bureau of Reclamation, and others. The section of river between Shoshone Falls and Niagara Springs has been closed to all access, and the Idaho Fish & Game Commission closed the area to fishing, hunting, and trapping.

The treatment plan was discussed at a Town Hall Meeting held on Sunday, Oct. 1 in Twin Falls, and ISDA Director Chanel Tewalt described the control efforts as “the most aggressive approach of any effort [to control these invasive species] in the U.S.” 

The treatment plan calls for the application of a copper-based pesticide product known as Natrix beginning Oct. 3. According to the Natrix label, “This copper product is toxic to fish and aquatic organisms.” As a result, all fish, plankton, shellfish and vegetation in the 6-mile treatment area are expected to die, with potential downstream mortality as a result of the oxygen depletion in the water as the material decomposes. Because the copper pesticide passes through the gills of fish, and does not accumulate in the tissue, it is not expected to negatively impact wildlife or birds that may consume the dead fish. As the river flows through the Hagerman and Buhl areas, spring flows contribute a significant volume of water that is expected to dilute the concentration of copper-based pesticides, thereby limiting direct mortality to aquatic organisms.

Dense mats of aquatic weeds (known as macrophytes) are an indication of too much phosphorous and other pollutants in the Snake River. Extensive weed beds will be killed by the pesticide application. Abby Urbanek photo.

Unfortunately, there do not appear to be any effective alternatives to the proposed pesticide application in order to eradicate the mussels before they get a foothold in the Snake. Based on the limited downstream spread of the mussels thus far, the state is hopeful that it will be able to wipe out this small population of invasive mussels with the copper-based treatment.

ICL continues to seek information on potential secondary mussel control efforts in the river, including the use of niclosamide (another pesticide) and pseudomonas (a biological control).

ICL is encouraging ISDA and other agencies to conduct in-depth monitoring to document the direct and indirect impacts of the Natrix application, and to closely consider the potential impacts of other follow-up treatments. 

Finally, ICL joins with ISDA and other state and federal agencies to urge Idahoans to respect the closure areas and to ensure that their boats are professionally decontaminated if they were in the Snake River in August or September. ISDA is offering free hot washes at the Twin Falls Visitor Center and at the Twin Falls County West Building (Mon-Friday, 8 a.m. – 5 p.m.).

Mussels can clog propellers, irrigation, hydropower, and other infrastructure. Tom Britt photo.

Where do we go from here?

ICL is concerned about the precedent this treatment effort may set. While we are hopeful that the aggressive treatment will be successful, in the event that it is not, we have significant reservations about expanding or repeating this treatment in the Mid-Snake or beyond, and  emphasize that each occurrence of invasive mussels warrants site-specific consideration. 

In many downstream areas of the Snake River, the presence of threatened or endangered species may limit similar types of treatment, so the best outcome would be for this treatment to be successful in eradicating these mussels. 

The proposed quagga treatment in the Snake River extends downstream from Shoshone Falls. ISDA photo.

Regardless of whether the treatment is effective, it should be evident to all Idahoans that we need to redouble our efforts to monitor for the potential introduction of mussels into Idaho’s waters. The location and effectiveness of boat check and decontamination stations should be closely evaluated by ISDA, the Governor, and the Idaho Legislature, and additional funding will be needed to carry out the program. 

In the mid-Snake River, additional investments will be needed to restore habitat impacted by the treatments, and to promote recovery. In addition, concerns with water quality in the mid-Snake River have long been a focus of ICL’s, and the discovery of these invasive quagga mussels in this section of the river provides an impetus to redouble efforts to restore the Snake to a healthy, ecologically functioning river.

For more information and ongoing updates regarding quagga mussels in the Snake River, visit ISDA’s official site at https://agri.idaho.gov/main/plants/snake-river-quagga-mussel-veligers/.

(This blog was co-authored by ICL’s Central Idaho Director, Josh Johnson and Governmental Relations Director, Jonathan Oppenheimer.)