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Thompson Lake is one of approximately 24 water bodies in Maine that have documented infestations of variable leaf milfoil. Variable leaf milfoil, an invasive species, is an aggressive plant, which, by forming dense mats of vegetation, crowds out native plants. Thick growth of this plant can ruin boating, swimming, and other recreational uses of a water body. The plant spreads mainly by fragmentation.

Maine has seven species of native milfoil, but it is the invasive variable leaf milfoil that causes most concern. It is most prevalent in shallower water up to 15 feet deep. While positive identification of the plant is not easy and should be left to the experts, variable leaf milfoil has some distinguishing characteristics. Its long stems with whorls of finely divided leaves are rooted in the bottom and rise vertically to the surface of the water. Near the surface, especially in shallower water, stems are typically red and may turn and grow horizontally, often forming thick mats. The plant has two distinct types of leaves. The submerged leaves are feather or comb-like, occur in whorls of four to six, and are one to two inches long. The flowers are small and reddish and form on the stem just above the emergent leaves.


Variable leaf milfoil first appeared in the southern section of Thompson Lake about 1980. At first confined to the part of the lake known as the Heath, it apparently spread into the main lake after the reconstruction of the causeway and culverts, which divide the main part of the lake, were reconstructed from the shallower Heath.

By 2005 the milfoil had spread from one end of the lake to the other, with the heaviest concentrations found in shallow areas, especially in the Heath, the Greeley Brook area, Otisfield Cove, Pine Point, Edwards Cove, and Parson's Point Cove (near Hancock Beach). Once established, the milfoil is difficult to control. After consulting with Maine's Department of Environmental Protection, TLEA's Environmental Committee, chaired by Scott Bernardy, decided to try eradicating the milfoil in limited areas by using benthic barriers. These essentially are heavy, opaque plastic tarps placed over the milfoil, and which remain in place for about two months. The effect is to smother the plants. Late in the summer of 2005, volunteers placed eight benthic barriers over the large milfoil infestation in Edwards Cove. Each of the ten weighted tarps covered about 800 square feet of lake bottom. Volunteers also placed benthic barriers with considerable success in Otisfield Cove.

In the spring of 2008, TLEA directors purchased a second-hand pontoon boat and then proceeded to turn it into a milfoil harvester, given the name "Hippobottomus." At the center of the harvester system is a vacuum pump mounted on the boat. A diver in the water hand pulls the milfoil and then uses a four-inch vacuum hose to deliver the milfoil to a sluice box, also mounted on the boat. The sluice box separates the plant material from the water and packages it into fifty-pound mesh bags. TLEA's boat was modeled on the one the Lakes Environmental Association was using on Little Sebago Lake.


TLEA mounted two capital campaigns to fund this ambitions endeavor.  The  result....since 2008

 208 tons of milfoil have been removed or smothered.

                                                                                   WHERE WE ARE NOW

TLEA's efforts towards eradicating the milfoil on Thompson Lake have yielded exceptional results.  To learn more click  HERE

To see photos of our milfoil efforts under way click HERE


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