Invasive species are on the move

Invasive species are organisms (plants, animals, or other living things) that cause ecological or economic harm in a new environment where it is not native. In their non-native range, invasive populations grow out of control as they lack natural predators, pathogens, and competitors.

7 Lakes leads the charge in invasive aquatics prevention, early detection, and remediation in the Belgrade Lakes watershed. Our robust Invasive Aquatics Program works closely with the Department of Environmental Protection and local lake associations to ensure that invasive species cause minimal harm to our lakes, so that they can be enjoyed by people and wildlife for years to come.

Our program is built on four foundational pillars that address every aspect of invasive aquatic species management:

• Prevention — Courtesy Boat Inspections that stop invasive species before they enter or leave our waters.
• Education — Programming for all ages focused on aquatic plant identification, survey methods, and the threats invasive species pose.
• Early Detection — Community-supported monitoring through Invasive Plant Paddles and Adopt-A-Shoreline surveys.
• Remediation — Targeted management and removal of infestations.

View Maine-DEP’s map of current infested waterbodies in the state.

Courtesy Boat Inspectors (CBIs; the friendly folks in yellow t-shirts at public boat launches) are the first defense against the spread of invasive aquatic species. As part of a state-wide initiative led by Maine-DEP, our CBIs are there to teach boaters on how to properly inspect all watercraft and equipment for invasive aquatic hitchhikers. The program provides an opportunity to connect and educate the community on the impact of invasive species as well as ensuring that boats do not become vessels for transport.

A team of paid and volunteer CBIs cover Long Pond, Great Pond, North Pond, East Pond, Messalonskee and Salmon Lake. This program is funded largely by local lake associations, as well as local towns, donors, and a cost-share grant funded by Preserve Maine Waters’ “Lake and River Protection” sticker.

CBIs ask boaters a few routine questions such as “where was the last waterbody this boat was used in?” to understand how and where invasive species are spreading. All CBI data is available to the public on Maine-DEP’ CBI Dashboard.

The statewide dashboard displays the number of boat inspections conducted and indicates whether any invasive aquatic species were detected. Use the drop-down menus on the left side to filter results by specific lake, date range, or organization.

View Past Years Data

View 2023 Data

View 2024 Data

View 2025 Data

To become a paid or volunteer CBI, please email Invasives Coordinator, Josie Miller.

What is the Adopt-A-Shoreline “pledge?”

1. Attend an invasive aquatic plant identification course

Plant ID workshops are held weekly at our office from June-September. Workshops are ~1 hour long. Attendees receive hands-on plant ID training and instructions on how to survey.

2. Survey your adopted shoreline twice a season

Surveys can be conducted via kayak, snorkel, motorboat, and paddleboard. Ideally, volunteers will conduct two surveys a year- one in the summer and one in the fall.

3. Report back and let us know what you found!

The most important part of the Adopt-A-Shoreline program is communication. We want to hear from you! Have you seen anything new growing up around your dock? Have you seen a plant with feather-divided leaves around? Let us know!

Invasive Aquatic Plant Control

Our team of certified SCUBA divers are permitted through Maine-DEP and receive extensive training on invasive plant removal to ensure safe and effective results. We are currently managing two invasive aquatic plant species in the watershed:

1. Curly-leaf pondweed in North Pond and East Pond
2. Variable-leaf milfoil in Great Pond and Messalonskee Lake

Since remediation work began in East Pond’s Serpentine, we have seen a decrease of 89% in curly-leaf pondweed biomass from persistent manual removal methods. After applying a one-time herbicide application to the infestation in Great Pond’s Great Meadow Stream, we have seen a decrease of 99% in variable-leaf milfoil biomass. Our crew checks each infestation on a weekly basis from May – October.

All of our remediation work is shared with Maine-DEP and is available for the public’s view at the link below.

Invasive Aquatic Plant Control

7 Lakes Alliance diver use a combination of physical plant removal, benthic barrier installation, and targeted herbicide to manage invasive aquatic plants.

For physical removal—or as we say “weeding the garden underwater”—one to two divers breathe via surface-supplied air and are supported by a boat tender and an additional surface support person in a paddlecraft.  Having a paddler directly above the diver has proven highly effective for fragment containment, safety, and real-time communication between the diver and tender.

Physical Plant Removal

The exact removal depends on the type and location of the infestation:

• Stream Infestations (e.g. Great Meadow Stream):
  Typically, two divers zig-zag from shore toward the stream center, searching for invasive plants. When a plant is found, it is removed immediately unless it is part of a large, dense patch that requires additional effort or coordination.
• Open-Water Infestations (e.g. North Pond):
  Surveys are first conducted from paddleboards or motorboats, with individual plants marked using homemade buoys.  Unless a large patch is identified—where two divers can work simultaneously from opposite ends—operations usually proceed with a single to allow for greater mobility.  The diver can easily move between buoys or be dive-towed to distant locations as needed.
• When invasive plants are found at low density, widely scattered, or in very shallow water, divers remove each plant by the root and place it directly into collection bags.
• When plants are found at higher densities and in water at least three feet deep, divers remove them by the root, but the material can be fed into a suction hose and processed by a boat tender. This method, known as Diver Assisted Suction Harvesting (DASH), increases efficiency by reducing how often a diver needs to surface.  However, DASH equipment is costly to maintain and not suitable for every type of infestation.

Benthic Barriers

Benthic barriers are materials—typically tarps or rolls of burlap—placed over rooted plants to block sunlight and suppress growth.  Maine DEP regulations require that no more than 10% of any area be covered at one time to ensure natural processes and wildlife remain undisturbed.  Barriers are intended to be removed or relocated every six months, unless the barrier is constructed of biodegradable materials like burlap.  Once the invasive plants beneath them have died, the barrier is removed, allowing native species to naturally recolonize the exposed sediment.

Barriers are used selectively depending on the invasive species, substrate type, and site conditions:

• Curly-leaf Pondweed (CLP): Benthic barriers are not used for CLP because it responds well to hand-harvesting.  The roots of this species are relatively shallow and can be removed easily and effectively by divers.  Additionally, the reproductive structures (turions) of CLP remain viable longer than any benthic barriers that may cover them up.
• Variable-leaf Milfoil: Benthic barriers are used for milfoil, which has deeper and more resilient root systems.  They are especially helpful in clay or compacted substrates, where complete root removal is difficult through hand-pulling alone.
• Substrate: Many infested areas in the watershed have loose, mucky sediment that accumulates plant debris.  In these locations, benthic barriers are not used because they cannot be securely anchored and may shift, potentially damaging motorboats or other equipment.

Herbicide Treatments

Aquatic herbicides are one of several tools used to manage invasive aquatic plants when infestations are too large or dense to control through physical removal alone. While the term “chemical treatment” can raise concerns, modern aquatic herbicides are highly regulated, carefully applied, and designed to minimize risks to people, wildlife, and native plants.

Most in-lake treatments today use low-risk, targeted products that are absorbed primarily by specific invasive species and break down quickly in the environment. These treatments are conducted by licensed professionals under strict state permits and monitoring requirements.

One commonly used systemic herbicide is ProcellaCOR© (active ingredient: florpyrauxifen-benzyl), a synthetic plant hormone that selectively targets milfoils and other fast-growing invasive plants. The product underwent extensive review by the U.S. Environmental Protection Agency before being approved for aquatic use, and the Maine Department of Environmental Protection (DEP) authorized its use in the state waters in 2019.

Herbicide treatments are not intended to eliminate all plants. Instead, they reduce invasive populations to manageable levels, allowing native plants to recover and enabling long-term control through monitoring and follow-up management.

Herbicides are typically considered when:

• Infestations are widespread or extremely dense.
• Physical removal methods are no longer effective or practical.
• Rapid reduction is needed to protect lake health and usability.
• Long-term management plans are in place.

In Maine, herbicide treatments are coordinated with the DEP and are often part of a broader integrated management strategy.  7 Lakes Alliance works closely with state partners to evaluate when and where herbicides are appropriate, including large infestations such as those in Belgrade Stream and Messalonskee Stream.

Surveys

7 Lakes Alliance conducts annual Level III (full-perimeter) surveys on all seven lakes in the watershed to search for the 15 Most Unwanted Invasive Aquatic Plants —a priority list developed by DEP based on each species’ potential ecological impact and likelihood of reaching Maine.

Most surveys are carried out by trained 7 Lakes staff, with additional support from volunteers through public Invasive Plant Paddle events, often co-hosted with local lake associations.

Waterbodies with known infestations are surveyed more frequently than noninfested lakes.  Active management sites may be monitored continuously throughout the growing season in coordination with removal efforts to track regrowth and detect new patches early.

Community members can play an important role in early detection and monitoring.  Opportunities to get involved include:

• Participating in an Invasive Plant Paddle.
• Adopting shoreline through the Adopt-A-Shoreline program.
• Requesting marker buoys to help flag plants at ongoing management sites.

Early detection and consistent monitoring are critical for protecting lake health and enabling rapid response when invasive plants are found.