The Minnesota Department of Natural Resources on Friday confirmed it has found larval zebra mussels from one of three sites on Lake of the Woods, a disappointing turn of events in the ongoing spread of aquatic invasive species.

While no adult or juvenile zebra mussels have been reported, the number of larvae is substantial, the DNR said. DNR crews detected the larval zebra mussels, called veligers, from a site in Muskeg Bay on the western side of the lake near Warroad, Minn., said Phil Talmage, area fisheries supervisor for the DNR in Baudette, Minn.

“It’s one of those things with the way they’ve been spreading around, I can’t lie – it wasn’t a huge surprise,” Talmage said. “But we were kind of hoping the longer we could go the better, obviously. But they’re here now.”

Recent DNR analysis of large lake zooplankton monitoring samples showed from four to 186 zebra mussel larvae, said Heidi Wolf, DNR invasive species unit supervisor. DNR crews haven’t detected veligers at the two other sampling sites on the Minnesota side of the lake near Zippel Bay and Long Point, Talmage said.

Talmage said he couldn’t speculate on the origin of the veligers or whether adults will become established in the lake. The veligers were found as part of a routine sampling effort and were confirmed last week, he said.

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Invasive species are sometimes introduced in a lake from connected waters or tributaries rather than human transport directly into the lake, the DNR said. Bowstring Lake, in the Big Fork River watershed, is listed as an infested water for zebra mussels.

The Big Fork River is a tributary of the Rainy River, which flows into Lake of the Woods.

“They were already in the system, so whether they came from transporting in or upstream sources, I figured they were going to arrive here. So now the big thing is to wait and see,” Talmage said.

With Friday’s news, the DNR will add the Minnesota portion of Lake of the Woods to the infested waters list for zebra mussels, so that people who harvest bait, fish commercially or use water from the lake take necessary precautions.

Other lake users should follow the same “Clean, Drain, Dispose” steps that are always legally required on all Minnesota water bodies, regardless of whether they are on the infested waters list, Wolf said.

“We really want to make sure we’re preventing the spread, which is the most effective thing we can do,” Wolf said.

The DNR and other agencies will continue to monitor Lake of the Woods, in part to learn more about how the lake’s water chemistry affects zebra mussels. Zebra mussels need calcium to form their shells, and lower calcium levels in Lake of the Woods could hamper that formation, Talmage said.

That’s the hope, at least.

“We don’t know if the lake’s water chemistry is conducive to zebra mussel survival,” said DNR research scientist Gary Montz. “It is possible that calcium levels or other factors might prevent propagation.”

In the meantime, Talmage said the DNR will continue to monitor Lake of the Woods, both for the presence of adult zebra mussels and changes in water clarity, which generally increases in waters where the invasive species becomes established.

They also interrupt the lower end of the food chain.

“They impact the system largely by impacting the base of the food web,” Talmage said. “That can have dire consequences if you get a huge shift in that. We’ll be continuing to monitor and really keeping our fingers on the pulse of the fishery and doing our diligence.”

At 70 miles long and 70 miles side, Lake of the Woods is the sixth largest freshwater lake located in or partially in the United States, after the five Great Lakes. Most of Lake of the Woods is in the Canadian province of Ontario, and a portion extends into the province of Manitoba. Between the U.S. and Canada, Lake of the Woods covers 951,337 acres and drains north into Hudson Bay, the DNR said.

Adults elusive on Red Lake

In related news, the DNR on Friday said adult zebra mussels haven’t been found in Red Lake, despite the finding earlier this year of veligers in water samples from both Upper and Lower Red lake.

Repeated occurrences of multiple veligers suggest zebra mussels are reproducing in Red Lake, but the adults may be difficult to find, given the large size of the lake, the DNR said.

Red Lake, at 288,800 acres is the largest inland lake in Minnesota. All but 48,000 acres of Upper Red Lake is located within the Red Lake Indian Reservation.

More info: mndnr.gov/invasives.

Dokken reports on outdoors. Call him at (701) 780-1148, (800) 477-6572 ext. 1148 or send email to bdokken@gfherald.com.