A boat used for surveying plants sits Monday on Cobbossee Lake in Manchester. A survey team recently found two large areas of the lake that are infested with Eurasian water milfoil. Officials have been trying to mitigate the spread of the invasive plant since 2018. Ashley Allen/Kennebec Journal

MANCHESTER — Efforts to rid Cobbossee Lake of invasive Eurasian water milfoil took a hit last week when a survey team spotted two large areas infested with the plant in Manchester.

The affected areas include part of the lake between the Outlet Bridge on Pond Road and a nearby dam, and an area past the dam, entering Cobbosseecontee Stream, according to the Cobbosseecontee Lake Association.

Courtesy of Cobbosseecontee Lake Association

The association has asked people to curb the spread of Eurasian water milfoil by avoiding jumping into the lake, swimming and fishing in the area along the shoreline. Officials are also discouraging people from using kayaks, canoes and boats.

“We are still in the early stages, trying to find the extent of it,” said Tom Mullin, executive director of the Friends of the Cobbossee Watershed, an organization tackling invasive species in the region.

Mullin said people will be deep diving to gauge the extent of the spread and to help plan a response later this week. Mullin’s organization, the lake association and the Maine Department of Environmental Protection are to meet to formulate a mitigation plan.

Friends of the Cobbossee Watershed, formed in 2001 to address invasive species, has been working with local lake associations to tackle milfoil popping up in lakes and ponds.


Eurasian water milfoil, native to Europe, Asia and northern Africa, is an invasive plant that, when introduced in a water channel, can spread rapidly, growing several inches in a day. So rapidly that it can restrict boat access and even obstruct people from swimming in the water.

An infestation of Eurasian water milfoil in Cobbossee Lake in 2021. Alex Dyer/Friends of the Cobbossee Watershed

If a fragment of the fragile yet aggressive plant is broken, by a boat, paddle, body part or fishing line, it can re-root itself and grow into a new plant. If the spread isn’t stunted, the plants can suck out the oxygen from a lake and have adverse effects on native species and marine life.

Cobbossee Lake, an 8.7-square-mile body of water that touches Litchfield, Manchester, Monmouth, West Gardiner and Winthrop, has been dealing with this invasive species for years.

Eurasian water milfoil was first spotted in Cobbossee Lake in 2018, and the Maine DEP applied an herbicide a year later in an attempt to wipe out the fast-growing plant. It reappeared in 2021 in the northeast quadrant of the lake.

Mullin said he is aware they cannot eliminate the invasive plant. It is man versus nature.

“But we are trying all we can to mitigate it. Every year, we do plant surveys, and folks on kayaks and paddle boards go in and search the entire lake,” said Mullins. “In addition to that, we have boat inspectors checking boats. Along the marina, we have certified inspectors doing inspections.”

If the plants occupy a small area, teams work to remove them immediately. But if they are in a larger area, like in the recent case, it takes more planning to identify the extent of the issue and how to respond to it.

Added Mullins, “The groups are working together on it to come up with a management plan.”

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