In 2018, a non-native plant called Eurasian Watermilfoil (Myriophyllum spicatum L. or EWM) was found in Cobbosseecontee Lake. Originally from Europe and Asia, this plant can rapidly spread through a body of water since it has no natural competitors. If left unchecked, an EWM infestation can have disastrous consequences. It can form thick mats that obstruct boating, fishing, and swimming. Moreover, it can decrease the lake water quality and lead to a decline in the value of shoreline properties.

     Control methods in Cobbossee have included manual removal of the plants, herbicide treatments, as well as annual surveys, and Courtesy Boat Inspections by trained staff and volunteers. As of 2023, EWM has now been found to be present in Cobbossee Stream. 

EWM - Cobbossee Outlet

Updated: 9/28/23

FOCW plant surveys and volunteer efforts have identified current areas of EWM growth in 2023.

  • Cobbossee Outlet by the bridge and dam
  • Cobbossee Stream
  • Horseshoe Island
  • Farr’s Cove
  • East Winthrop Public Boat Launch
  • Hammond’s Grove
  • Pine Point Lane
  • Upper Sister Island

To support our mitigation efforts, boaters and recreationists should steer clear of these areas. Activities such as swimming, paddling, and the use of boat propellers can cause the plants to break apart, which can lead to further infestations.

Plant Surveys will continue to determine the full extent of growth. Check the interactive map to see where AIS has been found in 2023.

A temporary Surface Use Restriction (SUR) is in place from the Pond Road bridge to the Dam. See the notice from Maine DEP.

Cobbossee Outlet - Pond Rd.

Moderately dense patches and singular plants of EWM have been found spreading from the lake side of the bridge, at the unofficial Manchester launch site, and to the dam. Actions have been taken to help mitigate the spread of the plants. An herbicide treatment was applied Friday, August 11th, see notice below.

In collaboration with the town of Manchester, a temporary fence has been erected to keep the public from inadvertently spreading these invasive plants while we work with the Department of Environmental Protection to remove the plants and return the outlet to its natural state. Until then, please avoid this area.

  • No swimming or jumping off the bridge
  • Keep your pets out of the water
  • Find a new location to launch kayaks and paddle boards for the time being
  • Do not fish off the bridge or to the dam

These are temporary measures while the plants are managed. Please reach out to the town of Manchester with any questions or concerns about this site, as it is town property. 

Herbicide Treatment 8/11

Maine DEP taking water sample in treatment area

An herbicide treatment took place August 11th, covering known Eurasian Water Milfoil locations just past the Pond Rd Bridge and to the dam. 

Maine DEP contracted with Solitude Lake Management for the professional application of ProCellaCOR, a selective herbicide. For more information on the organization or the herbicide used CLICK HERE.

The post-application procedure includes water tests to confirm that the herbicide dissipates within the appropriate timeframe. The first water sample was taken by DEP a few hours post-treatment. Another sample was taken the week of August 14th. No deviations from standard water quality were detected.

FOCW staff have been surveying the area to determine the effectiveness of the treatment, EWM plants are showing advanced stages of decay. FOCW and all our partners thank you for your help in avoiding this area to reduce the spread and help protect our lakes!

FOCW Surveyors checking the outlet post herbicide treatment

Links to our partners websites: