What is TLEA Doing About Invasive Plant Species?

Invasive plant species, such as variable leaf milfoil, are a growing threat to Maine lakes. Typically, these plants are introduced to lake via watercraft, as plant debris that clings to their trailers, anchors, propellers, or bilges is released and takes root. Once established, the plant colonies are often fragmented and set adrift by boat traffic resulting in infestation throughout the lake. The plants quickly crowd out the native plant species, which adversely affects the ecology of the lake and the available food sources for fish and wildlife. The plant growth is thick and slimy, making wading and swimming undesirable.

Variable leaf milfoil was first recognized in Thompson Lake in the 1980’s and was undoubtedly transported here by watercraft. Over 30 years, these relatively few colonies spread throughout the coves and shallow areas of the lake.

In 2005, concerned residents of the Otisfield and Edwards Cove areas began to mitigate milfoil in their section of the lake. They started a process of fabricating and deploying several 30’ x 30’ benthic barriers (tarps) to smother the plants.  They initially had good success, although confined to their small area. They realized the magnitude of the problem and sought the assistance of the Thompson Lake Environmental Association.

TLEA took over and expanded the program in 2007. We recognized that this required a comprehensive and long-term approach. We began networking with other lake associations to learn the best techniques for milfoil management. To fund this effort, TLEA applied for environmental grants and made direct appeals to lakefront property owners.  Contract divers were hired annually to do the work of hand pulling or suctioning milfoil from the waters, and to place the benthic barriers. A survey of the entire lake was performed, and a management plan was put in place to reduce, if not eliminate milfoil throughout the lake.

By 2016 most of the milfoil had been removed from the coves around the lake. However, a 10-acre area of infestation at the Pine Point remained that was too large for our removal methods. To avoid the fragmentation and spread of the milfoil a boat channel was created at Pine Point. However, this area of infestation remained the primary source for migration of milfoil to the rest of the lake. TLEA recognized that unless this area of infestation was removed much of the progress of the milfoil removal would eventually be undone.

In 2017 TLEA launched a capital campaign to remove milfoil from the Pine Point area and develop a long-term plan for invasive plant detection and removal. This effort was led by co-presidents Marcia Matuska and Kathy Cain. Our contributions have been diverse, with the majority coming from lakefront property owners and local businesses. We received support from the towns of Oxford, Poland, Otisfield and Casco. We also received grant revenue from the Maine Department of Environmental Protection. Most notably, TLEA received a donation of $25,000 from the Stephen and Tabitha King Foundation early in this campaign. As the graph below shows, the campaign raised over $400,000 dollars for this effort over 4 years. In addition, some TLEA members collectively donated $104,641 to our milfoil fund with their annual dues, putting us over the goal of $500,000 for this program.

We started this project by placing benthic barriers throughout Pine Point. The barriers, which smothered the plants, were placed over 1.5- 2 acre sections and rotated on a yearly basis, until the roughly 10 acre area was mostly cleared of milfoil. The crew also employed diver assisted suction harvesting (DASH) and hand pulling as needed. Eventually, boat traffic was restored in this area. In addition, we perform annual surveys of the entire lake to detect and remove invasive plants.

Our Milfoil Crew is presently a 3-person team led by Alex Bernardy, of Otisfield Cove. They work from our revamped pontoon boat, the “Hippobottomus”. This work horse of a boat has a suction harvester and an external air delivery system for divers as they locate and remove plants. Some days consist of hand pulling the plants from murky water in frigid temperatures. On good days, the crew is on the Hippo, diving with surface supplied air to locate and suction plants. The morselized plants are then packed into sacks and transported to outlying farms, where it is used for fertilizer. Recently the crew has concentrated on hand pulling of plants in the shallow coves, especially at the Pismo beach area and around the Oxford dam, which is the outlet of the lake.

TLEA is also working to prevent the introduction and transport of invasive species through our Courtesy Boat Inspection program. We station trained personnel at the public boat launches of the lake during the busy periods, to assist boaters in the inspection of their watercraft. This is an extremely important part of our effort to prevent invasive species, as one introduction can lead to an infestation. This program is funded through our membership dues, donations, and grants from the Maine DEP.

Our invasive species mitigation program is an ongoing effort to protect Thompson Lake. We have accomplished much, but the risk of re- introduction is always present. Even more invasive plant species such as Eurasian Water Milfoil have been detected in other Maine lakes and can be easily transported. Invasive animal species, such as Zebra Mollusks have infested many lakes in western New England and are heading this way. Remember to always inspect, drain, and dry all watercraft entering or leaving the lake. If you have a chance, thank a Courtesy Boat Inspector or our Milfoil Crew for their efforts.