“Overall, everything went according to plan,” said ISDA deputy director Lloyd Knight, calling the effort very detailed and aggressive.

They're not done treating the river yet. Next month, they will address what Knight called “ponds and potholes” – areas that are not in the riverbed but hold the potential for mussels.

One such pool near Pillar Falls is only about 20 to 25 feet in diameter but is 60 feet deep, Knight said.

Dates for the treatment are still being determined, but when they do take place, it will be on a much smaller scale than the recently completed effort, and the treatment will be carried out by hand.

The copper-based molluscicide, called Natrix, ended on Saturday after efforts began on October 8. The long treatment is important because quagga mussels tend to close up and essentially hold their breath as they try to survive the treatment, officials say.

Workers are still on the river, Lloyd said, collecting quagga mussel samples and measuring Natrix levels in the river.

The target rate was one part per million, and the primary focus was getting the treatment deep into the 100-foot-deep pools in the river, part of the river's unique geology.

ISDA Director Chanel Tewalt said Times News last week that the department was under pressure to eradicate the mussels this time, and it's treating it like it's its last chance.

“We’re doing everything we can because we have no intention of trying again,” Tewalt said.

ISDA will continue to conduct extensive sampling using advanced techniques.

These advances this year helped find veligers, the larval form of quagga mussels, in Twin Falls Reservoir above Twin Falls Dam. This area was not treated last year due to negative results.

ISDA officials believe quagga mussels may have been introduced into the middle of the Snake River when a boater discharged infested ballast water into Twin Falls Reservoir. No veligers were found above the reservoir, including Cauldron Linn, Murtaugh Lake and canal feeders.

Quick treatment of the mussels would not have been possible with the support of the public and others, Lloyd said. Idaho Power has allowed ISDA to use its facilities, and the treatment effort is widely supported by agriculture, including canal companies, because the cost of doing business would increase if quagga mussels took hold.

Access to the river from Hansen Bridge to Yingst Grade remains closed and the ISDA will later decide when to open the waters. Although the natrix level is one part per million below drinking water standards, Lloyd said the ISDA is cautious and it could take about a week for the amount of natrix in the river to return to background levels.

The dilution area extends downstream to the Kanaka Rapids north of Buhl.

Access to the river is already limited due to construction projects at Centennial Waterfront, Shoshone Falls and Twin Falls parks.

Lloyd said he appreciates the public's patience.

“I know they don’t enjoy these closures, they don’t enjoy dealing with them any more than we do,” he said.