Pacific Northwest
The quagga mussel, first discovered in the United States in 1989, is an invasive species that alters the food web by filtering water and removing plankton, according to the U.S. Geological Survey. | Amy Benson/U.S. Geological Survey

ID - After $3M effort, Idaho officials hope they killed off invasive quagga mussels in Snake River

TWIN FALLS (Idaho Capital Sun) — Idaho state officials are hopeful that the approximately $3 million effort to kill invasive quagga mussels detected in the Snake River in September was successful. But they don’t expect to know if they wiped out all of the mussels until waters warm up and water sampling surveys resume next spring.

The plan to kill the mussels involved treating a 16-mile section of the Snake River near Twin Falls with a copper-based chemical that was hazardous to mussels and fish and required state officials to airlift boats into otherwise inaccessible portions of the river.

Some state employees even camped on tiny islands and river banks for days on end in an effort to kill the mussels before they could reproduce rapidly, which state officials warned could clog pipes used for drinking water and irrigation, take over the hulls of ships and boats and alter recreation opportunities on the river.

“To our knowledge, it is the biggest treatment of its kind ever attempted in the United States,” Idaho Department of Agriculture Director Chanel Tewalt told a group of Idaho legislators Monday.

“We know doing nothing would have cost us a lot more,” Tewalt added.

Chemical treatments killed thousands of fish in the Twin Falls area

Officials from the Idaho Department of Agriculture, Idaho Department of Fish and Game and Idaho Parks and Recreation briefed the Idaho Legislature’s Natural Resources Interim Committee on the invasive mussels during a meeting Monday at the Idaho State Capitol.

While the officials don’t know if they successfully killed all of the mussels, they said they documented that the copper-based chemical they used known as Natrix started killing invasive mussels within 48 hours of the chemical being introduced into the affected sections of the Snake River.

Idaho Department of Fish and Game officials said the chemical killed thousands of fish in the Twin Falls area of the Snake River, with Fish and Games officials removing six to seven tons of dead fish that had floated to the surface of the river. The dead fish included at least 48 white sturgeon, the oldest of which were 35 years old and up to eight feet long, officials said Monday.

“We knew that doing nothing wasn’t an option, but the treatment came with downsides, for sure, and one of those that has been very visible is fish mortality,” Tewalt said. “We were very open that while fish mortality was unfortunate and none of us want to see it, if we don’t treat the river we lose the whole thing.”

Idaho Department of Fish and Game Director Jim Fredericks told legislators Monday that one of the department’s focal points moving forward will be restocking sturgeon in the area and rebuilding the fishery. Because the dead sturgeon came from a hatchery, they can be replaced. But Fredericks said some of the fish were up to 35 years old.

“You don’t replace those overnight,” Fredericks said.

Idaho House Majority Leader Megan Blanksma, R-Hammett, praised state officials for their response, saying they acted quickly and worked well together across different agencies.

“This is one of the best operations I have ever seen an agency accomplish,” Blanksma said, adding that as a downriver pumper and her agriculture operation depends on the Snake River.

Officials with the Idaho Department of Agriculture announced Sept. 19 that they had confirmed the presence of quagga mussel larvae in the Centennial Waterfront Park, the Idaho Capital Sun reported. Water samples also confirmed a higher concentration of the invasive mussels in larval form near Shoshone Falls.

In response, state officials asked the public to stay out of the water in the affected portions of the Snake River near Twin Falls, set up a series of free hot wash stations for boaters and rafters to clean their watercraft and developed the plan to treat the affected portion of the Snake River with Natrix between Oct. 3 to Oct. 13.

Tewalt estimated that it cost $1.3 to $1.4 million to obtain the chemical Natrix from the supplier SePro.

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