Newest invasive species spotted on Minnesota lakes puts squeeze on plants, fish

Minnesota can now add a new name to its growing list of invasive aquatic species — starry stonewort.

The Minnesota Department of Natural Resources said Friday that the plant, actually an algae, has been found in two connected lakes, Koronis and Mud, near Paynesville. Like Eurasian milfoil, it grows into dense mats that can cover the surface of shallow waters, squeezing out other plants and creating a wall between fish and their spawning grounds.

It's apparently been there for some time, too. It's grown to cover 53 acres of a shallow area on the southwest side of Lake Koronis near a public input site off Hwy. 55, and it's spread into the main basin and into neighboring Mud Lake.

"It's really hard to see this happening," said Karen Langmo, a member of the Koronis Lake Association whose grandfather built the family cabin there in 1927. "To me, this lake is sacred."

Langmo said that property owners on the lake have been struggling with excessive weed growth around the public input site for some time. It finally got so bad this year that the rotting plants began to smell and the Lake Association called in the DNR.

Chip Welling, invasive species coordinator for the DNR, said it took a while to confirm what the DNR feared. But it took an expert on starry stonewort to positively identify it.

Welling said the plant most likely got into the lakes from a boat that had picked up a plant fragment from a lake in another state. Given the size of the growth, that could have been some time ago, he said.

Langmo said it's especially disheartening because the Lake Association has an active inspection system for boats at its three public access sites, and the lakes have no other invasive species established. Not even milfoil. "It chokes out Eurasian milfoil, which is really scary," she said. "And zebra mussels like it."

Although it's on the list of invasive species that could show up in Minnesota, starry stonewort "wasn't at the top," Welling said.

So far, it appears the two lakes are the only ones in Minnesota that have been infested. The DNR has conducted a survey of other lakes in a 10-mile radius and found no trace of the plant, Welling said. But it's so well established in Koronis and Mud that it probably can't be removed by pulling it out by hand or using herbicides.

Starry stonewort, named for the tiny star shaped bulbils on its root system, has spread widely in Michigan, where it was discovered in Lake St. Clair in 1986. It was found for the first time in Wisconsin last year in a lake near Waukesha.

A plant that is native to Europe, and, surprisingly, endangered in England, starry stonewort most likely entered the Great Lakes watershed by ballast water discharges from freighters.

Welling said it's too soon to know how it will behave in Minnesota lakes, or how easily it will spread. "But clearly, we wish it wasn't here," he said.

In Michigan, where it has spread to some 250 lakes, it seems to like almost any condition — sand or muck, sun or shade — and prefers shallow water of 2 to 5 feet.

For Langmo, it's a bitter lesson in boat-owner carelessness that must change to protect the state's other lakes.

"It doesn't take that long to drain a live well, pull plugs and check for weeds," she said. "It's hard to understand why people don't want to do it."

Josephine Marcotty • 612-673-7394