New tactic in the fight against zebra mussels will be tested on Lake Minnetonka

The science lab is moving to Lake Minnetonka.

To protect the waters of the Twin Cities' largest and most popular lake from invasive species, researchers are using Minnetonka as the testing ground for a new study. Crews this week started testing low doses of a copper-based pesticide on zebra mussel larvae — called "veligers" — to kill them off and slow their spread.

It's the first study of its kind in Minnesota or nationally, and the latest effort in the battle against the state's proliferating mussels.

The results could help public agencies and lake advocates control the spread of the invasives on other lakes across Minnesota, shifting the focus from killing off all the pests to keeping their numbers at bay.

"People don't even think about it this way — the strategy is new," said Michael McCartney, a researcher and assistant professor at the Minnesota Aquatic Invasive Species Research Center. "You can knock them back a lot."

Researchers from the center and the Minnehaha Creek Watershed District are conducting the experiment, using the pesticide on six test areas. The study is funded by a $24,000 grant from Hennepin County, part of $325,000 in state funding that the county received for aquatic invasive species grants.

This week, crews are doing the first of three tests in Robinson's Bay in Deephaven, taking water samples to see how many of the microscopic veligers died from the copper applied the day before.

They'll repeat the tests next month, looking to see how low a dose is most effective at killing off the veligers.

"It has a lot of promise if it can be successful," said Eric Fieldseth, program manager for the watershed's aquatic invasive species program.

While the growth of the mussels has led some to feel the fight is futile, researchers counter that there remain many uninfested lakes in Minnesota.

This week's tests could help experts control the zebra mussel population in lakes that either aren't fully infested like Minnetonka or that have enclosed bays where the pesticide can't easily spread.

That could reduce the effect they have on the environment — and perhaps cut back on the money spent to do so.

It's a way to go on the offensive, while boaters continue state-required prevention efforts such as rinsing and draining boats.

"You wouldn't look to eradicate a lake this size, but you'd look to reduce the population," McCartney said, as his crew plied the waters of Lake Minnetonka. "It really nails these larvae."

The copper-based product, along with two other chemicals, was used to kill off mussels on neighboring Christmas Lake. But zebra mussels were later found outside of the treated area.

The fingernail-sized pest, which has become the poster child for aquatic invasive species, alters ecosystems. It crowds out native mussels and competes with other aquatic creatures for food.

Mussels also cling to boat hulls and docks, and their sharp shells create a hazard for swimmers.

More than 200 waterways in Minnesota are infested — including Lake Minnetonka since 2010 — with zebra mussels either in the water or closely connected to an infested waterway.

But the state says that's still less than 2 percent of Minnesota lakes.

Earlier this year, a watershed district study found that about 200,000 zebra mussels per square meter cover the bottom of just one of Minnetonka's bays — Wayzata Bay — where they thrive on the water's moderate algae levels and affect its quality.

Now, researchers say, they might be able to pinpoint when zebra mussels start to change a lake's ecology.

"It's not too late for Minnetonka," McCartney said. "One thing to say is 'That's it, it's all over,' or you can reduce the negative impact."

Minnetonka, the epicenter for boating in the Twin Cities, also has become the hub of groundbreaking research on invasive species.

In addition to the copper pesticide study, University of Minnesota researchers, a lake marina owner and boat manufacturer are looking at how boat designs could reduce how much water is left in places on the boat, like live wells that don't fully drain and which may permit veligers to spread when the boat is used on other lakes.

The watershed district and the U also are planning to partner with the U.S. Geological Survey later this year to do a lab evaluation of four different pesticides on zebra mussels from Lake Minnetonka.

And the watershed district is studying the genetic composition of hybrid milfoil on five of the lake's bays while wrapping up a study of common carp in the Six Mile Creek Subwatershed to Halsted's Bay on the lake.

"We're really on the cutting edge of this," said Telly Mamayek, spokeswoman for the watershed district. "We have a living lab right in our backyard."

Kelly Smith • 612-673-4141