Invasive starry stonewort found in Medicine Lake

Updated: 6:36 p.m. | Posted: 11:54 a.m.

The Minnesota Department of Natural Resources says starry stonewort, an invasive species, has been confirmed in Medicine Lake in the west metro.

It's the first new case of starry stonewort in the state this year. The aquatic invader is now confirmed in 12 Minnesota lakes.

Starry stonewort is a grasslike algae that can form dense mats that make boating, fishing and swimming difficult. It's named for the small, white, star-shaped bulbils that distinguish it from other look-alike native algae.

"This is a relatively new invasive species for Minnesota," said Keegan Lund, invasive species biologist with the DNR. "This is the 12th confirmation of its presence in the whole state. But it's also the first infestation in the metro, where it is there is a lot of use of our recreational lakes, a lot of activity, a lot of movement of watercraft, so the potential for spread is high."

Native to Europe and Asia, it was introduced to the United States in the 1970s through ballast water discharged by cargo ships on the Great Lakes.

Starry stonewort first showed up in Minnesota in 2015 in Lake Koronis near Paynesville. Since then, experts have been trying to figure out ways to control and treat the pesky species.

A Three Rivers Park District watercraft inspector recognized starry stonewort on a boat propeller and notified the DNR.

Invasive species specialists confirmed a widespread growth around the public access on the north end of Medicine Lake, the DNR said in a news release. A survey found starry stonewort in about 14 acres of the 924-acre lake.

"It's a relatively unstudied invasive species," Lund said. "There's still a lot we need to know. But has potential impacts like other invasive plants in that it can cause recreational nuisances, it can fill up the water column, it can replace native plants."

Lund said there's concern about the invader spreading to other Twin Cities lakes.

"It just takes a small fragment of the plant to potentially spread," Lund said. "We know that in some lakes, they can be quite a nuisance and can cause a lot of problems, so we want to make sure this infestation remains isolated."

The DNR and Three Rivers Park District plan to treat the area near the access. Starry stonewort has never been eradicated from any U.S. lake.

Other Minnesota lakes with starry stonewort include Grand, Mud and Rice lakes in Stearns County; Cass, Moose, Turtle and Upper Red lakes in Beltrami County; Lake Minnewaska in Pope County; West Lake Sylvia in Wright County; and Lake Winnibigoshish in Cass and Itasca counties.

Boaters can help stop the spread of invasive species by cleaning and draining their boats and trailers and disposing of unwanted bait before moving to another lake or river.