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With no cellphone towers, roads or permanent residents, this wilderness archipelago is about as remote as it gets.

Yet it’s still not isolated enough to evade a notorious Great Lakes villain.

That’s why Lauren Isbell and Alex Egan, National Park Service scientists by training, recently found themselves diving more than 20 feet deep in Lake Superior, scouring rocks and dock pilings for any sign of fugitive mussels.

After about a half-hour underwater, the pair resurfaced and Isbell thrust a parmesan cheese canister into the air.

“We got three,” she announced. “All adults.”

Tiny and unmoving in their plastic prison cell, the thumbnail-sized shellfish didn’t look like much to fear. But knowing what Isbell and Egan do — that invasive quagga and zebra mussels have 

destroyed entire ecosystems and killed billions of baby fish

 in the lower Great Lakes — it would be foolish to underestimate them.

Lake Superior is the lone holdout in a mussel invasion that has overtaken every other Great Lake, a salvation credited to low calcium levels that stymie mussels’ efforts to build shells, cold water that hinders their reproduction, and relative isolation, which limits the boat traffic that spreads invasive species.

But a spate of recent outbreaks, from Isle Royale to Canada’s Nipigon Bay, are testing old assumptions about the lake’s defenses and leaving scientists like Isbell with an uneasy feeling.

“We’re insulated,” she said. “but we’re not immune.”

‘I just hope that never happens to us’

Given the risks they pose, the ideal number of invasive mussels would have been zero. Yet the absence of babies offered hope of banishing the shellfish before they reproduce and do major damage to Isle Royale’s pristine underwater environment.

Much is at stake. In the three decades since European quagga and zebra mussels arrived in the Great Lakes via an oceangoing ship’s ballast water, they have taken over lakes Ontario, Erie, Michigan and Huron, hogging the nutrients and phytoplankton that once sustained native fish.

The crisis has rippled through the ecosystem, destroying fishing families’ livelihoods in the process.

“Thank God we still have a lot of whitefish in Lake Superior,” said Patricia Peterson, the matriarch of a fishing family in Hancock who has watched her downstate counterparts go out of business one by one.

“I just hope that never happens to us.”

At one time, scientists thought the Big Lake was largely immune to the mussel invasion.

Outbreaks in the busy shipping harbors of Duluth and Thunder Bay were viewed as little cause for concern. Warm, shallow water, calcium-rich river runoff and heavy shipping traffic there offer a foothold for mussels that is not found in the open water. Sporadic reports of mussels in the wider lake were written off as harmless strays from passing boats.

Outbreaks on Isle Royale in 2009, the Apostle Islands in 2011 and Nipigon Bay, Canada in 2017 were the first signs of deeper trouble. Drifting currents and unwashed boats seemed to be spreading the invasion to new territory.

Then, in 2022, new evidence sent a shock through the scientific community.

While conducting plankton surveys, US Environmental Protection Agency scientists found microscopic mussel larvae called veligers at several new locations in the lake. Further analysis revealed their DNA in more than 100 samples.

Now, scientists are racing to make sense of the discovery.

In a best-case scenario, the veligers were mere drifters that would never have survived to adulthood in the lake’s calcium-deficient depths.

After all, studies have found that those types of mussels, known as driessenids, struggle to build shells in water with less than about 20 milligrams of calcium per liter. Lake Superior averages 12 milligrams per liter.

Perhaps changes to the environment, such as increased precipitation caused by climate change, are causing calcium to pulse off the landscape and into the lake, creating new opportunities for invasive mussels. Or perhaps the mussels need less calcium than previously assumed.

“There’s a lot of genetic variability,” said Diane Waller, a scientist who works on invasive mussel issues for the US Geological Survey’s 

Upper Midwest Environmental Sciences Center

. “Could they be adapting over time?”

It’s a terrifying prospect for Katy Matson, a member of the Sault Ste. Marie Tribe of Chippewa Indians whose family has owned Matson Fisheries in Munising for six generations and fished in Lake Superior for far longer.

“My ancestors used to live on that island right there and go fishing,” Matson said, pointing to 

 just offshore of the Pictured Rocks National Lakeshore.

“It would be more than heartbreaking to be told that I couldn’t fish anymore because there’s not enough fish.”

Back on Isle Royale, parks staff are focused on protecting just one small corner of the lake.

 that visit the park yearly pose a constant threat of new infestations. Once, divers happened to be in the water to notice when an old-timey wooden tall ship sailed into harbor with invasive mussels clinging to its hull.

Park staff asked the sailors to leave, and they obliged. One crisis averted.

But in a park with no front gate, where visitors can enter from any direction, it’s not feasible to catch every infested boat.

Michigan and Minnesota both require boaters to clean aquatic organisms from their boats and trailers and drain all bilges and ballast tanks before launching into a new water body. But compliance and enforcement are both spotty.

“The sheer volume of vessels utilizing Michigan’s waterways does create a challenge,” said Joanne Foreman, a spokesperson for the Michigan invasive species program.

Stricter enforcement may not help Isle Royale much. Many of the park’s visitors travel from infested areas of Lake Superior itself, like Duluth, Minnesota.

Park ecologist Lynette Potvin said officials will soon write a biosecurity plan detailing contingencies for a widening outbreak. They’re also considering new ways to police visiting boats.

At Lake Tahoe, all boats are subjected to mandatory inspection and decontamination before entering the water. In the Everglades, boaters can’t get a permit unless they complete an online course that warns against spreading invasive species.

“Something like that could be worthwhile, because we do encounter people who just don’t know, or they’re so used to Lake Michigan being fully infested that it doesn’t even occur to them that we’re not,” Potvin said.

And then there’s the specter of climate change.

Though zebra mussels can survive in near-freezing water, they reproduce only when the temperature hits 54 degrees. Once a rarity in Lake Superior, that’s happening more often these days.

During Isbell and Egan’s recent dive, the water hit 55 degrees. Just warm enough for an adult mussel to produce 40,000 offspring, whose encroachment would threaten the native lake trout, whitefish and other species that have lived here for thousands of years.

For now, the hand-plucking method appears to be helping.

Annual invasive mussel discoveries have fallen from more than 3,000 in 2018 to a couple hundred nowadays.

“We go back to the same locations over and over again, like you would a weed in your garden,” Isbell said.

They take the captured bivalves back to the lab, measure their shells, then stick them in a freezer, where they’ll eventually die.

But staffing limitations make it impossible to monitor the entire archipelago for new outbreaks. Isle Royale has just two permanent natural resources employees and the Trump administration 

has proposed cutting the National Park Service payroll

Early detection efforts are also sparse in the broader lake.

“All the places we’re not visiting, are they getting deposited there?” said Seth DePasqual, the park’s cultural resource manager. “This is a vast lake. They could be many places we’re not aware of.”

Public apathy and ignorance also complicate efforts to keep mussels at bay.

Despite the damage zebra and quagga mussels have caused in the Great Lakes, many Isle Royale visitors seem to have never heard of them, much less how to avoid spreading them to new territory. Others believe a full-blown infestation in Lake Superior is inevitable and see no point in fighting it.

But to Isbell, every invasive mussel plucked from the water is one less opportunity for the species to explode in the Big Lake or find their way into Isle Royale’s pristine inland lakes.

“I’d much rather pull three mussels than 3,000,” she said.

Isbell knows it’s only a temporary solution. But while she works here, scientists elsewhere are 

She hopes to hold the line long enough for those breakthroughs to emerge.

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Author

Tiny and unmoving in their plastic prison cell, the thumbnail-sized shellfish didn’t look like much to fear. But knowing that invasive quagga and zebra mussels have destroyed entire ecosystems and killed billions of baby fish in the lower Great Lakes, it would be foolish to underestimate them.

Scientists wonder if Lake Superior can continue to avoid an invasion of mussels

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