When two divers were harvesting an invasive plant species from the bottom of Lake Dunmore last month, they noticed something else that wasn’t supposed to be there — a zebra mussel.
Prior to this year, Lake Dunmore had largely avoided contact with the invasive species that has been creeping into the state’s largest lakes since it was first discovered in Lake Champlain in 1993.
But what the divers found, and the state Department of Environmental Conservation later confirmed, was that nearly 200 adult zebra mussels had taken up residence in the Addison County lake.
The freshwater mollusks reproduce rapidly, and can cause serious harm to ecological systems and machinery like boats and drinking water intakes in local lakes.
Kim Jensen, the state expert on aquatic invasive species management, said when her department first received a picture of the Lake Dunmore specimen, they were immediately concerned that it could be a zebra mussel. So within the week, Jensen and her team prepared to go to the lake themselves to try and document the scope of the problem.
Jensen’s team made GPS checkpoints throughout the cove, where the divers first found the mussel, of places where they suspected zebra mussels were located. The cove is the lake’s public access point where greeters are stationed to check boats as they enter and exit the lake, to make sure no invasive species are being unknowingly transported from lake to lake.
After the team’s digital inspection, they put on snorkel gear to visually inspect and collect specimens to bring back to the office.
The following week, the Lake Dunmore Fern Lake Association contracted the divers to remove all 200 specimens via suction.
“The divers were very enthusiastic and eager to get as many as they possibly could, and whatever they harvested, they left in a bucket for us,” Jensen said.
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She said she and her team would be back at the lake tomorrow to pick up the mussels and bring them back to the lab to be tested, before ultimately composting them. That’s the protocol with most invasive species removal, she said.
Jensen said while they’re at the lake, they plan on testing the water for zebra mussel larvae, which they found in Lake Dunmore once before, in 1999. But she said since those larvae never reproduced, they suspect that the lake’s calcium levels are too low to support an adult population.
But Jensen said that’s not a risk they want to take, stressing how harmful the species can be for a water source like Lake Dunmore.
“They easily outcompete native mussels,” she said. “And nothing eats them, they’re not a food source for any native wildlife, so it upsets the balance of the lake.”
Once a zebra mussel population is established in a lake, she said, it can cause thousands of dollars in damage, with people having to unclog pipes and fix other underwater infrastructure.
But, Jensen said, research suggests that the greeter program that stops and inspects boats on their way in and out of lakes is incredibly effective in preventing invasive species from spreading. She said last year alone, there were more than 1,000 interceptions of species that would have otherwise made their way into Vermont’s lakes and rivers.
“I believe that’s the number one best practice to stop and mitigate any threat to our lakes,” Jensen said. “There’s a lot of research that suggests that.”
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