Minnesota has saved its most prized natural landmarks — towering old growth pines, dramatic waterfalls, pockets of native prairie — by protecting them within the state parks system.

Yet the water bodies that define the Land of 10,000 Lakes face the most immediate threats from warmer temperatures and invasive species. Aquatic biologist Peter Sorensen is floating an idea to protect Minnesota's true gems: the state's lakes.

He'd start with Lake Itasca, the still-pristine source of the Mississippi River.

"The window is closing," said Sorensen, a leader in the state's fight against invasive Asian carp at the University of Minnesota. "There are fewer and fewer places to save, and we still don't have any way of getting invasive species out once they're in. We have to put a few lakes aside while we can."

It's still unclear exactly what protections might come with a "state lake" designation. Sorensen, who has been proposing the idea to lawmakers, lake associations and environmental groups, would ask for three main rule changes: restrict fishing to catch and release, protect the shoreline and nearby watershed from future development, and, perhaps most drastically, ban nearly all outside boats from launching onto the lake.

The only boats allowed would be rentals or tour boats — those that would stay on the lake and never travel to infested waters where they could pick up destructive hitchhikers, such as zebra mussels or starry stonewort or Eurasian watermilfoil weeds.

The idea isn't entirely new. For several years the Minnesota Department of Natural Resources (DNR) has been preparing for climate change by creating a handful of "refuge lakes," waters that are remote and deep enough that biologists believe native species of fish that need cold water will be able to survive even as temperatures rise.

The DNR has not added public restrictions to its refuge lakes, but is trying to buy or protect at least 75% of the land around each lake to protect the quality of the water. Those shoreline and watershed protections, however, don't defend against invasive species.

As for banning outside boats on certain lakes? That has never been tried in Minnesota.

The idea is "intriguing," said Jeff Forester, director of Minnesota Lakes and Rivers Advocates, an advocacy group for lakes and lake associations.

It would help keep zebra mussels out of at least one lake, and could provide a sanctuary to keep strong populations of prized northern game fish like walleye, pike and muskies.

"We're all looking for ways to manage our fisheries and make our lakes more resilient in this dynamic and changing situation we're in," Forester said. "If this would give us a lake we could save for research and to learn from and to protect our fisheries, then I think it will get a lot of support."

Stopping invasive species

Sorensen is basing the idea off protected aquatic areas that have limited boat traffic and fishing to help save coral reefs and fisheries in the Atlantic and Pacific oceans. He's not aware of any state trying similar tactics in a freshwater lake.

The problem with the idea is that it would only stop one way invasive species spread to new waters, said Heidi Wolf, DNR invasive species unit supervisor.

"We don't have any strong evidence of how lakes became infected," Wolf said. "We do know in two cases that they were infected through docks or lifts. So closing down one potential pathway without addressing the others, I don't think it's a viable way and I don't know how it would be enforceable."

The state spends millions of dollars a year on boat inspections and educational efforts to get boaters to clean their boats, docks or other equipment before putting them in the water.

Yet, the mussels keep spreading.

They've been found in more than 480 water bodies since they reached Minnesota in the mid-1990s, and, despite recent increases in inspections and educational outreach, the rate of the spread seems to be increasing. They've infested nearly 100 new lakes, rivers and streams since 2019. This summer, the mussels were found in a third lake in Hubbard County, home of Lake Itasca.

Zebra mussels are particularly damaging because they're highly effective filters, sucking out and consuming the nutrients and smallest edible material in a lake, robbing minnows and native organisms of essential food. In return, they excrete a carpet of waste that produces toxic algae. They also grow razor-sharp shells that can make beaches and lake fronts unusable.

Protecting the lake and access?

Identifying one or a few lakes that are particularly special or important to Minnesotans, such as Lake Itasca, and giving them extra protections is worthwhile, said John Rust, president of the Minnesota division of the Izaak Walton League, a conservation group.

"You don't want to create an extra burden on people fishing and boating, but it's possible even with checks and cleaning that zebra mussels slip through," he said. "Itasca is one of the most iconic lakes we have. You're not a true Minnesotan unless you've jumped across the rocks at the headwaters."

Reactions of lake associations have been mixed.

Itasca does deserve special protections, but blocking people from bringing in their boats might be going too far, said Sharon Natzel, president of Hubbard County Coalition of Lake Associations.

"It seems problematic to close off public access," Natzel said. "Hopefully we could try special requirements for cleaning or decontamination stations."

Sorensen is continuing his talks with lawmakers, hoping someone will champion "state lakes" in the next legislative session. So far, though, he doesn't have a sponsor.

The only reason Minnesota's tallest and oldest white and red pines surround Lake Itasca is because people had the foresight to create the first state park there in 1891, he said. Nobody could have predicted then that the lake would find itself surrounded by invasive species from all over the world.

It's fitting to create the first state lake in the same place now to deal with these new threats, Sorensen said.

"If we can't save Lake Itasca," he said, "I don't know that we can save anything."

Greg Stanley • 612-673-4882