Milfoil cleanup efforts last summer at Jug Stream and Cobbossee Lake. Image courtesy of the Friends of the Cobbossee Watershed

Despite previous efforts to eradicate it, the invasive Eurasian watermilfoil plant has once again been found in the northeast quadrant of Cobbossee Lake, also referred to as Cobbosseecontee.

The 8.7-square-mile lake reaches Litchfield, Manchester, Monmouth, West Gardiner and Winthrop.

The plant was first discovered in the lake in 2018. It can spread quickly, growing inches per day, and once it overtakes a body of water, the tangle it creates at the surface prevents most swimming or boating.

It could also negatively impact native plant and animal life.

“A lake that becomes really infested is absolutely useless to everybody,” said John Stanek, vice commodore of the CYC Lake Association. “There’s no boating or swimming.”

The association, formerly known as the Cobbossee Yacht Club, focuses on the preservation of the lake.


The group recently established a Eurasian Milfoil Eradication Fund to fight the plant with herbicides. Such treatments can cost $85,000.

In 2019, the Maine Department of Environmental Protection attempted to wipe out the plant with ProsellaCOR, a selective herbicide that specifically targets certain invasive plant species.

A recent infestation of Eurasian watermilfoil at Cobbossee Lake is treated June 23. Photo by Alex Dyer of Friends of the Cobbossee Watershed

The green pest was nevertheless discovered again in late 2020, according to Toni Pied, director of membership at Friends of the Cobbossee Watershed, an organization dedicated to protecting and improving the lakes, ponds and streams in the watershed.

“My plant survey team found some plants adjacent to, but outside, the original infestation area, and it was a pretty significant population,” she said of a discovery in June.

According to Pied, the Maine DEP got in touch with New England Milfoil, a company that specializes in removing the plant from New England lakes and ponds. New England Milfoil manually removes variable leaf water milfoil, and SOLitude Lake Management works with the Department of Environmental Protection to apply herbicide.

Since then, Pied said the Eurasian watermilfoil has been discovered in two more areas: On Hersey Island and Weston Brook, the inlet flowing from the Augusta Country Club golf course in Manchester.


It is unclear how the Eurasian watermilfoil first made its way into the lake. Both Pied and Stanek said they are not aware of any boat inspectors finding the plant on a vessel.

The plants commonly accumulate on anchors.

Though the current infestation is relatively small, Pied said it could become a big problem if left unchecked, as it grows fast and spreads quickly.

“Pretty much any place where the leaves attach to the stem is an area where a new plant could grow,” said Pied. “So if the wind, an animal, a boat, or a swimmer were to break up that plant, all of those little pieces could potentially grow a new plant. That’s a major way that milfoil is spread, and that’s why it’s such a problem. If you break up the plant, you can make hundreds of new plants.”

A recent infestation of Eurasian watermilfoil at Cobbossee Lake is treated June 23. Photo by Alex Dyer of Friends of the Cobbossee Watershed

Pied said the plant can overtake any area of the lake where the sun is able to penetrate to the bottom, meaning it could overtake almost half of the lake.

“So conceivably, if it was left unchecked, it could grow around the whole shoreline of Cobbossee Lake and most of the islands,” she said.


Once the watermilfoil takes over, the water quality suffers and the infected areas become stagnant, breeding mosquitos. Pied said there are examples of the invasive plant species negatively impacting property values.

A 2010 study uncovered that the presence of Eurasian watermilfoil can reduce the value of adjacent properties by one to 16%. A subsequent study from 2014 said that a watermilfoil infestation can lead to a 19% decline in property values.

Stanek said there are approximately 900 property owners along the shore of the lake.

In addition to fundraising, meant to pay for additional herbicide treatments, Stanek said he and others in the lake association are making a point to speak with elected officials in the five surrounding towns.

“We want to let them know what’s going on with that lake. Paying for boat inspections, which we’ve been doing for years and years and years, hasn’t caught it. It got by us somehow.”

Pied said she and her team will continue to monitor the lake.

“The important lesson here is that herbicides are not a silver bullet,” she said. “It’s one of the tools in our toolbox that we can use for this particular plant, but the importance still lies in preventing new plants from getting into the lake.”

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