Lake Koronis launches aggressive starry stonewort attack

PAYNESVILLE — A thick mat of starry stonewort has kept Michael Mackedanz from swimming in Lake Koronis this summer. It's wrapped around the propeller of his boat motor. It's made it difficult to use his lift and launch his pontoon.

"I like to swim. I like to go in the water. Personally, I think, ‘Do I have enough water in my well to clean off after I’ve gone in the lake looking the way it does?’ It’s not necessarily funny,” Mackedanz said.

The Minnesota Department of Natural Resources confirmed the state's first invasion of the aquatic invasive species last August in Lake Koronis, which straddles the Stearns-Meeker county line. Besides interfering with boating and other recreation, starry stonewort can smother fish spawning habitat.

The infestation had expanded into 250 acres on Lake Koronis before anyone noticed. For that reason, the DNR decided to manage, not eradicate.

The Koronis Lake Association took a more aggressive approach. It's spending $50,000 this summer on a three-part, DNR-permitted treatment, which will be followed by five years' worth of assessments. If treatments work, as soon as next year the KLA would roll out the rest of its $828,600 plan to treat more of the lake.

On Wednesday, Mackedanz, 67, a retired bread delivery driver and a full-time lakeshore resident since 1975, stood on shore near his house, watching a conveyor belt dump heavy mounds of the grasslike macro alga into a trailer.


Dockside Aquatic Services owner Matt Riehm of St. Paul pitched starry stonewort to the back of the trailer as Eco Harvester operator Bret Mayhew ran the machine. All told, they'll remove more than 140,000 pounds of the aquatic invasive from the test site, 6 acres on the northeast shore enclosed by a fine mesh net to prevent broken bits of the plant from spreading.

Because starry stonewort is so heavy — it's about 95 percent water — the harvester collects for only about 10 minutes at a time. Riehm took his turn at the controls, slowly maneuvering back into the netted area, looking for the spot where harvesting left off. It's not hard to find.

The site looks a bit like an underwater alfalfa field, harvested vs. unharvested areas as clearly defined as if a haybine were working a field. But this plant is rootless. When large mats interconnect, Riehm said the machine can pull in weeds from a 20-foot radius without moving.

He lowered the roller at the front of the machine until it drew the green matter from the water like giant clumps of hair from a drain, pulled it across a moving metal grid and deposited in onto a rubber belt that Riehm moved farther back as the holding area filled.

Kevin Farnum, the KLA member who's applied for the grants that fund the project, said he spent hours inspecting the Eco Harvester for invasive species, both plant and animal, before he allowed it onto Lake Koronis.


The harvested starry stonewort was transported to a farmer's property where it will lie in a compost heap. Farnum said the KLA avoided public compost sites to keep the invasive out of circulation. The University of Minnesota and other researchers are still getting a handle on its viability. Farnum said he also inspected the dump truck before it left. (It's covered with a tarp in transport.)

Late this week, scuba divers were scheduled to remove by hand the starry stonewort that the mechanical harvester missed. Then the invasive will be allowed to grow for a few weeks. Finally, chemicals will treat regrowth from remaining fragments and bulbils, the star-shaped structures that give the alga its name.

"I hope it succeeds," Mackedanz said later by phone from Big Fish Lake north of Cold Spring, where he was working for the DNR as a watercraft inspector, looking for aquatic invasive species on boats entering and leaving the lake. Taking on those duties reflects his perspective on Lake Koronis.

"There’s a problem there, and it’s just not the people that live on the lake —  it’s not just their problem. It’s everybody’s problem. I would say that 50 percent of the people or more that use the lake don’t actually live on the lake. And if it comes to the point where we can’t boat, we can’t do recreational things out on the lake, we're all going to suffer.”

The KLA has supplemented the DNR's scheduled watercraft inspection hours at the public access. It's marked a channel through the infested bay. It's added signs at the access. Still, Farnum said not much has changed since the infestation was confirmed Aug. 28, 2015.

“We have not seen a decrease in traffic, which is sad because you would think people would say, ‘Wait a minute. There is a compelling reason not to go to this lake,’” Farnum said.

Meanwhile, Chris Jurek, the DNR's Sauk Rapids-based aquatic invasive species specialist, said starry stonewort appeared to be expanding within the lake. Staff revisited 325 sample points first tested last year.


"It's expanding in Koronis," Jurek said.

Last year, starry stonewort was found in 17 percent of the sites; this year it was found in 30 percent. Meanwhile, the presence of native plants was down slightly. Muskgrass, for example, appeared in 59 percent of the sites, down 1 percent from last year.

Jurek said two years of data wasn't enough to establish a trend. Annual sampling will continue. Another treatment may be scheduled at the Minnesota Highway 55 public access on the southeast corner of the lake.

"We're starting to discuss another type of management action at the access going into the fall fishing season," Jurek said.

Starry stonewort most likely spreads from lake to lake when fragments are transported via watercraft.

Earlier this month, the DNR confirmed the state's second starry stonewort infestation, 185 miles north of Lake Koronis in Turtle Lake near Bemidji. On Aug. 25, the DNR confirmed two more: in Beltrami County's Upper Red and Cass lakes.

In all cases, the invasive was discovered near public accesses. Heidi Wolf, the DNR's invasive species unit supervisor, said invasive plants will act differently depending upon the water body. Variations also might occur from year to year, depending on factors such as water clarity.


"It hasn't been eradicated anyplace in the U.S. yet but we're going to try," Wolf said.

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The DNR reminds boaters to check watercraft for invasives, remove the plug and drain all water before transport, and dump all unused bait in the trash. Find more:

More online

VIDEO: See how the Eco Harvester works (it's one of three treatments aimed at killing starry stonewort on Lake Koronis):