Sad but necessary: How will mussel treatment affect Snake River?

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Warning signs are seen on the banks of the Snake River on Friday, Oct. 6, 2023, near Twin Falls. The Idaho State Department of Agriculture is treating the Snake River with pesticides to remove the invasive quagga mussels. Chicken Cutting Machine

Sad but necessary: How will mussel treatment affect Snake River?

A closure sign is seen Friday, Oct. 6, 2023, below the Perrine Bridge on the Snake River. The Idaho State Department of Agriculture is treating the Snake River with pesticides to remove the invasive quagga mussels.

TWIN FALLS — Last week, spigots were turned on and, gradually, thousands of gallons of molluscicide were intentionally released into the Snake River from the hydropower plant at the Twin Falls downstream to Centennial Waterfront Park in an effort to kill quagga mussels.

It shows that sometimes you have to harm something for it to survive.

It was an aggressive move, but state officials said they had no choice after quagga mussel larvae and an adult mussel were found in that section of the river last month. It was either that or let the small invasive pests slowly take over the waterway, clogging pipes and choking out wildlife.

“It is hard,” said Chanel Tewalt, director of the Idaho State Department of Agriculture, “and as hard as it is, it would be harder to have this river changed forever.”

A crew on a boat works on the Snake River.

Even though officials say the water will still be considered safe for humans to drink during the treatment, no one knows exactly how the river will be affected in the attempt to kill the larvae and mussels.

Fish and plant life will — and have — died. As of Monday, 20 hatchery-raised sturgeon ranging from 6 feet to under 2 feet, along with several hundred other fish, including largescale suckers, common carp, northern pike minnow and yellow perch, have been pulled from the river, although officials say mammals and waterfowl living near the river are not expected to be affected.

The treatment is expected to be wrapped up on Friday, after which there will be an evaluation conducted to determine its success. Everyone is holding their breath for a positive outcome.

It would be a huge step for ISDA to get life back to normal, including for recreation enthusiasts — boaters, kayakers, fishermen and hunters — who’ve been banned from the stretch of the river out of fear their activities could spread the mussel.

“We are very cognizant of the closures and people who want to get back to the river they love,” Tewalt said.

A tote containing Natrix is seen last week near Pillar Falls. The treatment is being used in an effort to kill quagga mussels.

Natrix, a copper-based molluscicide, which in May 2020 became an approved pesticide under the Federal Insecticide, Fungicide, and Rodenticide Act, is the chosen treatment and the first 96-hour phase of the procedure concluded last week.

A second treatment is now being applied from Shoshone Falls to Pillar Falls, the area where a plume of larvae was detected and adult mussels are suspected of hiding under the water, latched onto rocks or other surfaces.

Depending on the results of the initial 10-day effort, more treatment might be needed.

Once mussels mature, they quickly start reproducing. Each year, a female mussel can produce up to 1 million microscopic free-swimming larvae, called veligers. After a few weeks, the larvae begin to form shells and attach to firm, underwater surfaces.

The urgency is there to kill both adults and larvae and do it quickly.

Tewalt told a crowd at a briefing Oct. 1 at Twin Falls City Hall that under normal circumstances, the department would reach out to people to give them a chance to comment on a plan of action, but there was no time for that. The window of opportunity to have the best chance at killing the mussels is small, she said.

Idaho Code allows the state to make quick decisions when something is deemed an environmental emergency.

“There is no sitting around ...,” Tewalt said. “We get to work as quickly as possible.”

Employees of the Idaho State Department of Agriculture camp out along the Snake River so they can constantly monitor the quagga mussel treatment.

The stretch of the river near Twin Falls has become a battleground. It is not just a local issue; the future of the Columbia River Basin, the only major river system in the U.S. that had been free of the invasive pests, could be at stake.

Fish and Game biologists conduct a fish mortality survey on the Snake River in response to the quagga mussel treatment.

Gov. Brad Little said if the mussels got firmly established in Idaho’s waterways, it could cost the state $100 million each year in direct and indirect costs.

Mussel larvae were confirmed Sept. 18 after a routine sampling of water at Centennial Waterfront Park. Ten days later, a scuba diver found a single adult mussel at Shoshone Falls.

The discovery of the adult mussel was incredibly fortunate, officials said, equating it to locating a needle in a two-mile-long haystack.

But it’s not the only one down there.

“As soon as you find one, you know they can’t exist by themselves; there needs to be more,” Tewalt said.

When the adult was discovered, it added more urgency to the situation. There was no such luck as what Montana faced five years ago when veligers were found in a river in the central portion of the state, but no adults were ever discovered and the state officially remains mussel-free.

While coming up with the final plan, although officials were working quickly, corners weren’t cut, Tewalt said, and agencies were given a chance to comment.

Numerous state and federal agencies, offices and utilities — a total of 16 listed in a recent news release — were kept in the loop and officials gave advice and helped with the plan’s formulation.

Tewalt said the ISDA took a number of groups on the river to explain the situation and to discuss the scale and magnitude of the plan. The agency faced plenty of questions and plenty of different options were discussed.

As an announcement grew near, Tewalt recalled that the ISDA told them, “We need you all to tell us now if there is a problem with the treatment plan as we have constructed it collaboratively.”

No one objected, Tewalt said.

A display shows what an infestation of quagga mussels looks like.

Twin Falls Commissioner Don Hall said he has been happy with the accessibility to ISDA officials.

“I have been impressed with the team and their communication,” he said, likening it to having Tewalt on speed dial.

In addition, property owners were notified of the release of Natrix.

Natrix began to be released into the river on the evening of Oct. 3. A few issues, including doing some last-minute calibrations and fixing a broken hose, caused a later start than anticipated.

“It was normal stuff,” Tewalt said, “but we obviously wanted to make sure everything was right.”

Totes, each containing 250 gallons of Natrix, a pesticide used to eradicate quagga mussels, is seen last week near the Snake River.

As the initial wave of treatment was released, the water at Shoshone Falls began to take on a bluish color, but that was an anticipated, temporary byproduct of the release.

“It didn’t run blue for very long,” she said.

And in the first place, getting the amount of product to the river was not an easy task.

“Hats off to the manufacturing company for being able to work with us,” Tewalt said. “They didn’t just have this amount sitting on a shelf somewhere.”

The manufacturer, SePRO Corporation, ramped up manufacturing and rushed it from the East Coast to Idaho.

The trucks were tracked hour by hour, Tewalt said.

Workers set up empty 250-gallon totes along strategic parts of the river, and transported the product to the totes by boat. The chemical is also being dispensed on boats by the hired applicator, who has worked with ISDA in the past.

In addition, SePRO Corporation has chemists on-site to ensure it is applied appropriately.

“They know their product better than anyone,” Tewalt said.

The target rate of one part per mission was reached a day or more after the applications began.

From its initial release, “every piece of that is very carefully calibrated to get us to 1 ppm in a way that is measured and in a way that is appropriate and fits with the plan that is laid out,” Tewalt said.

ISDA employees are camped out on the river, monitoring and finetuning the treatment.

Releases were reduced once monitoring sites hit 1 ppm. The treatment was to last 96 hours to help ensure quagga mussels receive a lethal dose.

Varley explained at a briefing that mussels have a tendency to “hold their breath,” or close up, if there is something in the water that they don’t like, much like what children might do when offered broccoli.

Treating all the river at that 1 ppm can be tricky, Tewalt said, as the river is not all the same depth. There are also deep pools, including one near Pillar Falls that is 90 feet deep, which are being treated as a separate body of water, said Varley.

The total amount of pesticide used per treatment is about 11,000 gallons in each of the two sections from Centennial Waterfront Park to Pillar Falls, and from Pillar Falls to Shoshone Falls. An additional amount is needed to treat the deep pools. The area near Twin Falls hydroplant took a lesser amount.

Downstream from Centennial Park, on a dirt road leading to Auger Falls, are signs posted at nearly every potential point of river access, alerting people to stay off the river. They warn of danger and pesticides, along with mentioning the quagga mussel treatment.

Idaho Fish and Game fisheries biologists from across southern Idaho on Sunday and Monday used non-lethal electrofishing techniques in the Snake River to mark fish in three short reaches of the river.

Regardless of what kind of danger it may or may not pose, people have been told to stay off the river from the Twin Falls to Niagara Springs for weeks, so they shouldn’t be in the river, Tewalt said.

The amount of Natrix being added to the river will keep it safe to drink, officials say, as the drinking water standard is 1.3 ppm, Tewalt said. The product starts killing fish, however, at a rate of 0.4 ppm.

“This copper product is toxic to fish and aquatic organisms. Unlike most organic pesticides, copper is an element and will not break down in the environment and will therefore accumulate with repeated applications. Copper is a micronutrient, but its pesticidal application rate exceeds the amount of copper needed as a nutrient,” warnings on the Natrix label reads.

Fish kills have been documented so far, and Tewalt said organic matter in the river is showing signs of breaking down.

“We love the sturgeon,” Terry Thompson of the Idaho Department of Fish and Game said. He’s never caught one of the huge sturgeon in the river but knows people who have.

“For people who catch them, it is quite the memory,” he said.

He said he wasn’t sure if larger sturgeon stand a better chance of surviving the treatment, and that very few of the sturgeon on the stretch of river are native.

The best chance of fish survival could depend on them finding water sources coming into the river, so they could escape the toxic levels, Thompson said, noting that has been happening. But the river is more than fish and plant life. Native mussels such as the Western pearlshell are in the river and expected to take a hit.

Thompson said Fish & Game is running two boats on the river 12 hours a day, documenting fish mortality. He expects the department will be monitoring fish kill two weeks after the treatment.

Mary Anne Nelson, with the Idaho Department of Environmental Quality, said the department doesn’t know how long it will take for the river to heal.

Fish & Game will look at restocking options after the treatment is over.

“I don’t like the killing of fish in that stretch of the river,” Commissioner Hall said. “But I like it better than to let the mussels infiltrate the river. What those mussels will do is 1,000-fold worse.”

Due to the presence of quagga mussels at larval life stages in the Centennial Waterfront Park area of the Snake River, the Idaho Fish and Game director has declared an emergency and has closed fishing of any kind on the Snake River from Twin Falls Hydroelectric Dam to the bridge crossing the Snake River at Idaho Highway 46.

If the river wasn’t treated, a quagga mussel infestation would end up fouling the ecosystem, leading to fish kill, officials said.

The molluscicide doesn’t settle into the flesh of the fish, but travels over the gills so they cannot breathe, preventing the fish from being able to take oxygen out of the water and into their bloodstream, officials said.

The two 96-hour treatments, with a short period of time in between, are done to keep within the label directions, Varley said.

The pesticide won’t suddenly disappear from the environment, but officials say it will dissipate as springs pour into the river downstream, as well as bubble up from under the river.

In addition, plant life is expected to die as it absorbs the copper and suspended sediment also absorbs copper.

Canyon Springs Road is seen Friday, Oct. 6, 2023, in the Snake River Canyon below the Perrine Bridge north of Twin Falls. The Idaho State Department of Agriculture is treating the Snake River with pesticides to remove invasive quagga mussels.

The product is expected to dissipate by 70% within a 16-mile stretch downriver of Centennial Waterfront Park, as springs flowing into the river will aid in the dilution process.

The rate at Centennial Park is about 380 cubic feet per second and increases to about 2,000 cfs at the Highway 46 Bridge north of Buhl, Varley said.

Having to do the treatment is “heartbreaking,” Tewalt said.

But one thing is certain, Tewalt said.

The plan calls for using a copper-based treatment in an effort to eradicate the mussels, which could cost Idaho hundreds of millions of dollars if they establish themselves in waterways.

In response to the recent detection of invasive larval quagga mussels in the Snake River at the Centennial Water Park in Twin Falls, Idaho Fish and Game is temporarily closing water access to the public on lands owned and managed by Fish and Game along the Snake River effective Sept. 21.

"An invasion of the quagga mussel is potentially disastrous," Twin Falls Canal Co. Manager Jay Barlogi told the Times-News on Wednesday.