Beneath the calm surface of Lake Koronis, a war is being waged against an invasive algae threatening the health of this popular recreation spot.
Starry stonewort first showed up in Minnesota in 2015 in Lake Koronis near Paynesville. Since then, experts have been trying to figure out how to get rid of the pesky species.
But the grasslike algae has now spread to eight other Minnesota lakes, where it can form dense mats that make boating, fishing and swimming difficult.
Because it's a relatively new invader, not a lot is known about its impact, said Dan Larkin, an extension specialist at the University of Minnesota's Aquatic Invasive Species Research Center.
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"There's cause for concern," Larkin said. "We've seen in Koronis and other places that it can be certainly a nuisance to lake users and lakeshore property owners, and can interfere with recreation."
Starry stonewort has never been eradicated from a U.S. lake. But Koronis residents were hopeful that an early, aggressive approach would be effective.
Using state grant dollars, local funding and private donations, the lake association developed a pilot program to test different treatments. Last summer they tried mechanical harvesting, a chemical algaecide and a combination of both.
The results were mixed. The algaecide did reduce the starry stonewort's biomass. But it didn't kill the white stars known as bulbils that are the reproductive part of the plant. In fact, Larkin said the density of bulbils actually increased.
"What we think might be happening in the exposure to the algaecide is a stress on the plant, and it responds by investing in reproduction," he said.
Obviously, this was not the result lake advocates were hoping for. Larkin said more research is needed to understand the findings.
"All the information we can gain at this point is vital," he said. "These Koronis test plots really provide a lot of information that can really be followed up on in more places to refine the approach that's used in management."
Although starry stonewort has been in the United States since 1978, there's relatively little data on how to manage it, said Dr. John Rodgers Jr., who directs the ecotoxicology program at Clemson University in South Carolina and has been advising Koronis residents.
"There's a lot of publications on where is it and how do we think it got there, but there's very little on intervention," Rodgers said. "That's the critical nature of this particular project on Lake Koronis."
It's possible that starry stonewort could be in other Minnesota lakes where it hasn't been confirmed yet, Rodgers said.
"It may be spreading, unfortunately, more than we think," he said.
Koronis residents say the algae is spreading to more parts of their lake. In some places, it's too thick to fish or get a boat through.
Dick Johnson has lived on Koronis since 1958, when his parents built a lake home on its shores. He said he's worried about the effect of starry stonewort on the lake's future.
"We just enjoy the lake, and our goal is to have the lake be enjoyable for our kids and our grandkids," he said. "And with starry stonewort, it's a problem."
Johnson said Koronis residents are concerned not only about controlling the invasive algae in their own lake, but stopping it from traveling elsewhere.
"We really don't want to spread it around our lake more, but we also are concerned about the other lakes," he said. "We don't want a whole bunch of lakes infested."
Kevin Farnum, who leads the lake association's invasive species efforts, said they plan to try more treatments this summer.
"We don't like the idea of using chemicals," he said. "We know there are people on the lake who are dramatically opposed to it. But simply sitting back and doing nothing isn't a good answer."
By using a mechanical harvester first before applying the algaecide, Farnum said they were able to get more chemical down into the starry stonewort where it was more effective.
"It's not like a vascular plant, where if you're in your garden and you treat it with Roundup, you treat the leaves and it will kill the whole plant," Farnum said. "In the case of starry stonewort, you have to kill every individual cell."
One thing researchers are studying is why Koronis seems to be particularly good at growing starry stonewort. That information could help predict what lakes the algae might turn up in next.
Efforts to prevent starry stonewort from spreading will be ramped up this summer. The U of M and the Department of Natural Resources will train citizens to identify invasive species like starry stonewort.
The goal is to have more "eyes on the water," said Chris Jurek, invasive species specialist with the DNR.
"The earlier you detect an aquatic invasive plant, sometimes it's easier to manage or prevent the spread," she said.
However, starry stonewort can be tricky to identify, Jurek said.
"It does take some practice and skill. There are a lot of look-alikes," she said.
On Aug. 5, volunteers will fan out across Minnesota and Wisconsin for Starry Trek, a one-day search for the algae.
Experts believe that boaters spread starry stonewort from lake to lake. Inspectors will be out at public accesses again this summer checking boats and trailers.
Some Koronis residents say the DNR isn't doing enough. They're frustrated that the agency didn't act quickly enough to close the public access where starry stonewort was found and still allows fishing tournaments on the lake.
Jeff Forester, executive director of Minnesota Lakes and Rivers Advocates, said western states like Montana and Idaho have stricter rules about inspecting and tagging boats crossing the border.
"It's conceivable that if the Legislature had shut the borders ... we wouldn't have starry stonewort in the state today," Forester said. "We need to get a lot more serious about this."
Until that happens, volunteers like Farnum will keep working to prevent starry stonewort from spreading elsewhere.
"You hate to lose a lake. If you lose a lake, it's gone," he said. "There's no eradication. There's no cure."
Starry stonewort across Minnesota
Since 2015, populations of starry stonewort have been confirmed by the DNR in 9 Minnesota lakes. The confirmed infestations are clustered around Beltrami and Stearns counties.
Starry stonewort summit
Dr. John Rodgers Jr., who directs the ecotoxicology program at Clemson University, will discuss starry stonewort at a summit from 1-3 p.m. April 22 at River's Edge Convention Center in St. Cloud. The event is open to the public.