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Invasive Curly-Leaf Pondweed Update

As the Belgrade Lakes Watershed prepares for its population to double from seasonal residents and visitors, there is one population that is rapidly decreasing: curly-leaf pondweed.

Curly-leaf is an invasive aquatic plant native to parts of Europe and Asia that was unintentionally brought to North America by cargo ships. Unfortunately, this tenacious invasive plant has been found in two waterbodies in the Belgrade Lakes.

Like most invasive aquatic plants, curly-leaf lacks natural predators and competitors that keep it from spreading out of control. What sets curly-leaf pondweed apart from most aquatic plants is that it grows over winter and is dormant during the summer and early fall, when most water recreation is occurring. While many of our seasonal residents will never encounter curly-leaf due to its unusual growth cycle, native aquatic plants and wildlife suffer from the overabundance of curly-leaf growth due to competition over space, sunlight, and nutrients in the late spring, when native plants are just beginning to wake up from their winter dormancy. Curly-leaf pondweed reproduces primarily through turions, a type of winter bud that can remain dormant in lake sediments for up to five years and rhizomes, horizontal roots that send out “runners” like strawberry plants.

Just before Memorial Day weekend, the 7 Lakes Alliance’s Invasive Aquatics team discovered several large patches of curly-leaf pondweed near the public boat launch in North Pond, Smithfield Maine. Removal efforts began immediately as the plants were already at the surface of the water and ready to drop dozens of turions per plant. By June 10th, the rooted curly-leaf in North Pond started to show signs of decay. At the same time, the algae that has been haunting North Pond since 2018 started to rise from the sediments, making the visibility for divers removing plant material particularly challenging. Despite the unfavorable diving conditions, 7 Lakes divers were able to remove all of the curly-leaf found. By June 18th, the entire perimeter and ~50 feet offshore of North Pond was surveyed.

Fortunately, it appears (for now) that the curly-leaf infestation is isolated to the north end of North Pond. Specifically, some scattered patches were found on the west side of Pomleau Island and several large patches were found East of Pomleau Island to Leech Brook Cove. Given the size of the patches and the abundance of turions attached to the rooted plants, this new infestation is not likely to ever be eradicated from North Pond. We will, however, be able to manage the invasive plants in North Pond by removing new shoots growing from turions in November. All plants missed during the fall cleanup will be removed in April, before the plants mature and produce new turions. Since curly-leaf primary spreads through turions, depleting the cache of turions in lake sediments and preventing the generation of new turions is the best way to control the infestation.

Meanwhile, the curly-leaf infestation in The Serpentine, the stream that connects East Pond to North Pond, is showing no signs of decay and follows a completely different growth pattern than the population found in North Pond. Since removal efforts began in The Serpentine, we have seen an 89% decrease in curly-leaf growth. This impressive decrease in the original infestation has been achieved by continuously weeding the infested area via SCUBA before the plants are able to produce new turions, excellent outreach and communication efforts by our partners at East Pond and North Pond Associations, and the financial support of the Maine Department of Environmental Protection. These fundamental tools for success will be used to control the curly-leaf in North Pond going forwards.

Unlike the infestation in The Serpentine, the curly-leaf in North Pond has been found in areas of high motorboat traffic which makes this infestation at high risk of spreading throughout North Pond and the watershed. While our divers can minimize the spread by removing plants before they grow tall enough to reach the water’s surface, the best way to prevent the spread of all invasive species between waterbodies is to follow Clean, Drain, Dry practices. Clean off all boating and fishing equipment that contacts lake water before using the equipment in another waterbody. Drain your bilge in the tie-down area as you exit a boat launch, and if possible, allow your equipment to fully dry between trips.

If you are concerned about curly-leaf pondweed and all invasive aquatic plants, please join our team! Volunteers are always welcome to cover Courtesy Boat Inspector shifts at the public launches, survey for invasive plants (group paddles and independently), and donate to the cause. Weekly aquatic plant identification workshops will resume June 26th, every Wednesday 10-11 AM at 7 Lake’s headquarters. Please email to get involved!


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