Why a Minnesota Lake Has Become a Giant, Living Laboratory

A Minnesota lake has become a giant, living laboratory to study invasive plants. Starry stonewort was found for the first time in our state in Lake Koronis in 2015. The aquatic invader has now spread to 13 Minnesota lakes.

Koronis is a 3,000-acre lake in Stearns County. When starry stonewort was discovered three years ago it had already taken over 250 acres; it has since doubled in size.

"It grows incredibly fast," said Koronis Lake Association board member Kevin Farnum. "It'll never go away. And that's not untypical. Most of your aquatic invasive species, you know once they're in a lake there's not really an eradication."

According to Farnum, the Koronis Lake Association has spent half a million dollars on a pilot project to get a handle on starry stonewort.

"Now the good news with that is in some of the areas we've been trying to manage is that we have had some significant reduction," he said.

When 5 EYEWITNESS NEWS visited Lake Koronis, auditors were on the water checking results of experiments. They document everything.

"We are trying to get the word out about what we're doing," said Farnum. "What our successes are, what our failures are, the timing, the mass of area, it's all important to control."

The auditors were pulling up huge gobs of the weed with rakes. According to the Minnesota DNR, starry stonewort is a bushy, bright green macro-algae. It produces a characteristic star-shaped bulbil. It grows from the bottom up and gets so thick that it chokes out native plants and fish habitat. That makes it difficult to swim in or drive a boat through it.

The Koronis Lake Association has learned the only way to stop invasive plants from spreading lake to lake is to make sure boats and trailers are clean.

And early detection is key because smaller infestations are easier to manage. To do that, the lake association purchased a weed puller. It rips roots from the lake bed in shallow water and chops plants off in deeper water, which makes herbicides more effective.

"At Koronis we're really learning while doing," said assistant professor Dan Larkin, from the University of Minnesota's Aquatic Invasive Species Research Center. "Lake Koronis is where starry stonewort was first found in the state. And we're learning a lot about the biology of this species, the impacts that it has where it invades and also how to try to manage it."  

Scientists at the university are zeroing in on the role chemicals play. Master's student Rafael Contreras showed 5 EYEWITNESS NEWS the starry stonewort he is growing to study.

"So this is a bulbil right here which is the reproductive organ of starry stonewort. We're trying to figure out the best herbicide at the best concentration for it to be killed," he said.

All the work in the lab at the university and in the giant living lab on Lake Koronis is aimed at protecting all our state's lakes.

"There's just tremendous uncertainty about what the future looks like. How many lakes in Minnesota will have it 10, 20, 30 years from now," said Larkin.

"No one is doing anything as much as we are as far as this combination of pulling and chemicals," said Farnum. "No one is doing as large of an area, thank heavens they don't have this large of an area to deal with. But I think it's going to be at the forefront of what do you do?"

Early detection is key to stopping aquatic invasive plants and autumn is the best time to spot starry stonewort. If you see it the Minnesota DNR wants you to report it.  

The state Legislature has allocated $10 million a year to combat invasive species. Aquatic Invasive Species Prevention Aid is a specific purpose aid distributed at the county level. The proceeds from this aid must be used solely to prevent or limit the spread of non-native, aquatic species at water access points within the county.