New aquatic invasive found in Lake Minnetonka

By Nicole Brodzik
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A new aquatic invasive species, a hybrid milfoil, has been discovered in both Lake Minnetonka (pictured) and Christmas Lake. (Nicole Brodzik/The Laker)
A new aquatic invasive species, a hybrid milfoil, has been discovered in both Lake Minnetonka (pictured) and Christmas Lake. (Nicole Brodzik/The Laker)
With aquatic invader numbers on the rise in Minnesota waterways, lake-goers should be on the look out for a new invasive plant species that could take over one of Minnesota’s biggest lakes.

A new study from the Minnehaha Creek Watershed, Montana State University and University of Minnesota has found a new hyrbid milfoil in both Lake Minnetonka and Christmas Lake. The new hybrid is believed to be a cross between Minnesota native northern watermilfoil and the invasive Eurasian watermilfoil.
The new crossbreed appears to be more resistant to treatment and control measures, according to the study, as more of this particular watermilfoil appears in areas that were treated with herbicides than those not being treated.

“Certain plants just develop stronger characteristics to survive these conditions,” MWCD AIS Program Manager Eric Fieldseth said. “Throughout the lakes, the hybrid seem to be more common, especially in bays that are being treated.”

As to how or why the hybridization is occurring, researchers are still unsure. Fieldseth said he’s not aware of any other hybrid species like this in these lakes, but said it’s been seen with watermilfoil before.

It’s difficult to identify from it’s native parent species, but lake goers could see large mats of what look like long branches covered in thin, green appendages, almost giving the appearance of pine tree branches. Even though half of the DNA from this new species is technically a native plant, the MWCD still considers the hybrid to be an invader. With spring and ice melt in the not so distant future, the watershed district asks that boaters and lake goers treat any watermilfoil mats with caution.

“We ask people to treat it like they do any other invasive,” Feildseth said. “Avoid driving your boat through the big matted areas. It’s not only bad for the lake and helps spread those plants, but it’s bad for your boat, too.”

The DNR also warns of boats helping to spread invasive species. According to the DNR website, milfoil can get stuck in boat propellers, trailers or water sports equipment and the segments of these milfoil species can begin growing in new waterways if boats are not cleaned properly.

“We ask people to continue to clean their boars and trailers of all vegetation whenever they leave the lakes,” Fieldseth said. “We hope this study helps the people managing these species to think about how complex it is and to look at the genetic makeup when completing treatment.”

Researchers have been studying the species for the last two years thanks to a $35,000 grant from Hennepin County. The hope is to expand this kind of research to neighboring states in the future.

For more information on the study, visit