Wednesday, February 1st, 2023
Wednesday, February 1st, 2023

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Another step forward in battle to kill Christmas Lake’s zebes

Shorewood, Minn. — Even with a sheet of ice capping Christmas Lake, the attempt to thwart a zebra mussel infestation has moved on to the next phase.

Officials planned to use augers to drill holes in the lake and apply liquid potash, or potassium chloride, on Friday, representing the latest volley in what has turned into a considerable effort to keep the unwanted invasive mussels from becoming established in this 267-acre west metro lake.

Potash isn’t federally approved for use as a pesticide, so the partnership working on this issue sought help from U.S. Sens. Amy Klobuchar and Al Franken, as well as U.S. Rep. Erik Paulsen. The U.S. Environmental Protection Agency granted a special exemption for Christmas Lake and Independence Lake, near the Hennepin County town of Maple Plain.

“They all supported it,” said Harley Feldman, treasurer of the Christmas Lake Homeowners Association. “It’s one of those things you kind of want to get done as soon as possible because time doesn’t work in our favor. That’s why we asked for their help.”

It probably won’t be known until springtime whether or not this treatment, which had to be pushed back a few days because of poor ice conditions, was successful in the goal of completely killing off all remaining zebra mussels in the lake, said Eric Fieldseth, aquatic invasive species specialist with Minnehaha Creek Watershed District.

“The real test is going to come as soon as the ice is off and we’re able to get back in there and do a very thorough sweep of the area,” Fieldseth said.

In September, the lake became the first in the country to be treated for zebra mussels with a pesticide called Zequanox, an expensive product that had just been approved by the U.S. EPA for open-water use. 

Previously, Zequanox had been tested only in open water as part of research and used in enclosed systems such as power plants.

While no living zebra mussels – there were about 5,000 in the area initially – were found inside the 50- by 60-foot containment barrier erected where the mussels were discovered, another 25 mussels were found outside the enclosure afterward.

Careful examination of boats and boat docks that were removed from the lake this fall in anticipation of winter turned up no additional zebra mussels, which like to cling to these types of objects, Fieldseth said.

The 25 zebra mussels found after the Zequanox treatment were removed by hand, but their discovery forced more action – and a larger containment barrier to be erected.

It only made sense to try Zequanox in the first place because the mussels were discovered very early following their arrival in the lake, thanks to an intensive monitoring program carried out by the Minnehaha Creek Watershed District. That initial treatment, for about 3,000 square feet of water, came at a cost of about $6,800 just for the pesticide. But, with the new containment area, which expanded the treatment to about 40,000 square feet, the cost to treat that much water with Zequanox would run about $100,000, said Keegan Lund, a Minnesota DNR aquatic invasive species specialist.

Zequanox isn’t effective in cold water.

Potash is both inexpensive and effective in these winter temperatures, but the DNR needed special federal approval to use it, since it isn’t approved for use as a pesticide, because it is indiscriminate in the mussels it kills.

“The population of native mussels in that area is very small,” Fieldseth said.

And in the meantime, as the groups waited for approval for potash, the lake was treated in October with copper sulfate. It isn’t known if that was successful.

“We were not certain (potash) would be approved, so we used the next material available,” Lund said.

Because of frequent monitoring, the species was discovered before the lake had become infested, and the City of Shorewood shut down the public access to the lake in August and it had remained closed since then.

Brad Nielsen, Shorewood’s planning director, said the city hoped to reopen the ramp to foot traffic only this week.

“There’s a lot of guys that are chomping at the bit to get out on the lake,” Nielsen said.

But before the lake can be opened to snowmobile, ATV, and vehicle traffic, Nielsen said, the city is working on a way to funnel traffic over the containment barrier, which will remain in place until the lake thaws out in spring.

“We don’t want that barrier damaged,” Nielsen said.

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