Treatments on Christmas Lake kill off zebra mussels

Researchers have successfully eradicated zebra mussels in a small area of a west metro lake, a feat unduplicated anywhere else in the U.S. in the fight against the invasive aquatic species.

Divers searched Christmas Lake last week and found no evidence of zebra mussels in an area near the lake's boat launch after crews used three different treatments on the area near Lake Minnetonka last fall and winter. It could mark the first time zebra mussels have been eradicated from a Minnesota waterway, though future tests will be needed to make sure the mussels have been completely eliminated, the state Department of Natural Resources said Monday.

The success story could also provide lessons for other Minnesota lakes and rivers infested with the fingernail-sized pest, which can damage boat motors, slice swimmers' feet and threaten fish populations.

"If these infestations are found early enough, we have treatments we can use. And in the right scenarios, they may work," said Keegan Lund, aquatic invasive species specialist with the DNR, adding that they are "cautiously optimistic" about the Christmas Lake case.

The lake, which is in parts of the cities of Shorewood and Chanhassen, became the first in the nation last fall to use Zequanox to get rid of zebra mussels; the product is made from dead bacteria that kill zebra mussels when they eat it.

Then crews used a copper treatment on the lake, followed by an injection of 1,000 pounds of potash, or potassium chloride, in December — only the third time potash has been used for zebra mussel control in the country.

"Minnesota is being a real leader in pushing for this and trying this in open water," said Michael McCartney, a research assistant professor in the Minnesota Aquatic Invasive Species Research Center at the University of Minnesota.

The DNR, which did the work along with the Minnehaha Creek Watershed District, city of Shorewood and University of Minnesota researchers, had to get special federal emergency permission to use the potash and copper treatments. But that quick action, partnership and early detection of the invasive species proved worthwhile.

"It's the best news we can have," said Craig Dawson, director of research and monitoring for the watershed district. "At this point, we have every indication we did the best job we could."

The infestation was discovered at the end of the summer, thanks to the watershed district's early detection program.

Two staffers monitored 12 lakes last year, Dawson said, doing searches of the shoreline and surveys of the lake. That helped the watershed district discover the infestation before it became less isolated, closing off the area immediately.

"It's a very unglamorous part of management, but it's a critical one," Dawson said, adding that this year, four staffers will monitor 30 lakes in the west metro.

On Christmas Lake, the work isn't done yet. Dawson said it takes five years without any sign of zebra mussels to be taken off the DNR's list of infested lakes.

So starting in May, the DNR and watershed district will continue doing searches along the shoreline and in the 267-acre lake to monitor and determine if zebra mussels have been completely eliminated from the lake.

While the lake's successful treatments could be a turning point in what has long been a losing battle to control the invasive species, officials say the treatments are too difficult and costly for larger lakes and ones that are fully infested, like Lake Minnetonka. The three treatments cost about $9,000 total for the less-than-1-acre area near the lake's boat launch, Lund said.

However, the information from Christmas Lake will help the DNR respond to future isolated infestations of zebra mussels in other lakes, better determining when, where and how to treat it more effectively, Lund said.

More than 200 Minnesota waterways are listed as infested by the DNR, but only 90 of those water bodies were listed because zebra mussels were found in the lake or river; others were listed as infested because the river or lake was connected to a waterway with zebra mussels. Now, when another waterway becomes infested, there's hope, McCartney said, for a positive outcome.

"The lesson is, act quickly," McCartney said. "If you act quickly, you can have a great impact."

Kelly Smith • 612-673-4141

Twitter: @kellystrib