SHOREWOOD, Minn. (AP) — Officials said Thursday they’re encouraged with initial results from an effort to kill zebra mussels infesting Christmas Lake west of Minneapolis.

The Minnehaha Creek Watershed District used the bacteria-based pesticide Zequanox to treat the area around the public boat access on the suburban lake earlier this month. The district said Thursday that it appears to have killed all the zebra mussels in the 50-foot by 60-foot treatment area.

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“We have more work to do to improve the long-term chances of containment, but these early results are encouraging,” Craig Dawson, director of the district’s aquatic invasive species program, said in a statement.

Divers found and removed around 25 more live zebra mussels outside that area last Friday. Officials now plan to expand the containment zone, and they’re considering alternatives to Zequanox, which isn’t as effective in colder water.

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Christmas Lake was selected for the test because the infestation was detected early. Officials said it marked the first use in the nation of Zequanox except for some small experiments or to kill the pests in power plant water pipes.

“We’re committed to doing everything we can to ensure total containment and, if possible, eradication of the zebra mussel infestation in Christmas Lake,” Keegan Lund, an invasive species specialist with the Minnesota Department of Natural Resources, said in the statement.

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