Every week through the warm months, a surveillance boat and a diver work their way across Suncook Lake in Belknap County, while kayakers and paddleboarders slip out at dawn, when the surface is glassy enough to see down into the water. They are not sightseeing. They are hunting a plant. For years the volunteers of the Suncook Lake Association have poured countless hours and tens of thousands of dollars into beating back variable milfoil, an aquatic invader that has quietly reshaped one of the region’s beloved water bodies. As New Hampshire Bulletin reported in its June 16 account of the statewide fight, the lesson emerging from lakes like Suncook is sobering: once an invasive plant is established, eradicating it is close to impossible.
That matters far beyond a single shoreline. New Hampshire is a state defined by its water. Lakes anchor summer economies, property values, tourism, and a sense of identity that runs from Winnipesaukee down to the smallest pond. When those waters fill with dense mats of non-native plants, the consequences are not abstract. Swimming becomes unpleasant, boating becomes difficult, fish habitat degrades, and the dollars that flow into lakeside towns each summer come under pressure. Understanding why this fight is so hard, and where it can still be won, is essential for anyone who cares about the Granite State’s most valuable natural resource.
A Problem Spread Across Roughly 100 Water Bodies
Suncook is not an outlier. According to the New Hampshire Department of Environmental Services, the lake is one of about 100 water bodies in the state with a known infestation of an aquatic invasive plant such as milfoil or another non-native species. Brea Arvidson, director of programs for the nonprofit NH LAKES, cautioned that the true figure is almost certainly higher, because many infestations have never been formally reported.
The plants thrive here for reasons rooted in biology. Invasive species like variable milfoil and curly-leaf pondweed carry traits that let them outcompete native plants: rapid growth, prolific seed production, and, critically, the ability to regenerate from a single broken fragment. That last trait makes them maddening to control, because a stray piece dislodged during a removal effort can drift off and start a brand new colony. Lee Petruk, one of the Suncook volunteers, described the emotional weight of watching this unfold. It is hard, she said, “to watch your lake change in your lifetime.” Her assessment of the group’s progress was blunt: “We’re not making progress. We’re keeping it at bay.”
Two forces accelerate the spread. The first is human. Boats, trailers, and fishing gear ferry plant fragments from one lake to the next, which is why prevention programs focus so heavily on inspecting watercraft. The second is climatic. Warmer waters and more nutrient-rich conditions give these aggressive plants an even sharper edge over the native species that normally keep a lake’s ecosystem in balance. David Neils, who administers the water management bureau at the Department of Environmental Services, framed the stakes plainly. “If you just let them go, they will become dominant,” he said. “They could affect the ecosystem, and they could affect peoples’ enjoyment of the water body.”
The Math of Control Is Brutal
There is no cheap or permanent fix. Surveillance paired with physical removal, either hand-pulling plants or using a large aquatic vacuum to suction them off the lakebed, is one approach. But once an infestation goes widespread, that kind of manual weeding becomes too big a job to finish. At that point managers may turn to herbicides, especially when the problem is severe and covers a large area. Even that carries trade-offs: plants can develop resistance, and the chemicals can have downstream effects. As Arvidson put it, no control method is perfect and most are costly.
The dollar figures tell the story. Hiring a diver to inspect a lake and pull plants is the cheapest option, often a few hundred dollars per session, according to Elizabeth Harper, executive director of the Lake Sunapee Protective Association. More intensive treatments such as herbicide application or suction harvesting can run into tens of thousands of dollars per treatment. And these are recurring costs, not one-time bills. At its June 3 meeting, the Governor and Executive Council approved state grants to local lake associations totaling $234,915 for work to hold invasive plants at bay across numerous water bodies. That money helps, and associations often pool resources and chase additional funding together, but Harper compared the effort to a never-ending game of whack-a-mole. The financial drain is the real constraint on what lake lovers can accomplish.
This is the same pattern of cost-shifting that has surfaced across the state’s environmental policy debates. Granite Staters have watched similar dynamics play out as federal rollbacks push new environmental and public health burdens onto state and local governments, and as communities grapple with the long tail of contamination in stories like the EPA’s retreat on PFAS drinking water limits. In each case, the burden of protecting water lands squarely on local shoulders.
Why Prevention Beats Treatment Every Time
If treatment is a losing battle once an infestation takes hold, prevention is where the real leverage lies. The front line is the boat launch. Through the Lake Host program run by NH LAKES, trained inspectors station themselves at public launches, teaching boaters what invasive plants look like and checking boats for hitchhiking fragments before they reach the water. State rules already require boaters to clean, drain, and dry their boats before moving between waterways, a point that Gov. Kelly Ayotte and New Hampshire Fish and Game law enforcement officers emphasized during a safe boating press conference on the shores of Lake Winnipesaukee on June 11.
When a plant slips past that first line of defense, the difference between success and failure comes down to speed and resources. A coordinated, well-funded, fast response can still eradicate an early infestation. A slow or under-resourced one almost never does.
Lake Sunapee Proves It Can Be Done
Lake Sunapee offers the rare success story, and it is instructive precisely because it shows what early detection makes possible. In 2024, a Lake Host stationed at a public launch spotted a single stem of curly-leaved pondweed clinging to a boat as it came out of the water. That one observation told the association the invasive species was present in the lake, and the response was immediate. Divers pulled every plant they could find that summer. A survey the following year turned up more, and those were removed too. This season, surveys by divers and a network of dozens of volunteer kayak weed watchers have found no evidence of the plant at all.
“Fingers crossed, but you know, as far as this goes, we feel like it’s been successful,” Harper said. “But, obviously, we have to remain vigilant.” It was not the first win for Sunapee. When milfoil appeared in its waters in 2001, a massive mobilization of volunteers eradicated it and gave rise to what is now the Lake Host program itself.
The contrast with nearby Baptist Pond, located upstream of Sunapee, drives the point home. There, curly-leaved pondweed was detected only a year or two later, and that delay was enough to make eradication no longer feasible. “That one we have not been able to keep on top of,” Harper said. The amount of time and money Sunapee invested to get ahead of its problem, she noted, pales in comparison to the larger, harder-to-estimate cost of simply letting the plants take over. These lakes are economic engines, and protecting them is, in the end, an investment in the towns and businesses that depend on a clean shoreline, much as the state’s broader summer tourism season leans on healthy lakes and mountains.
Arvidson summed up the underlying tension that every lake association faces. “The struggle with lake management in general is balancing the environment, the ecosystem, and the wants of the people around the lake,” she said. “Eradication, is it possible? For the most part, if money is not an issue.”
What Granite Staters Can Do This Summer
For the average lake user, the takeaways are concrete. Clean, drain, and dry any boat, trailer, kayak, paddleboard, or fishing gear before moving between water bodies. Learn to recognize the most common invaders, milfoil and curly-leaf pondweed, and report anything suspicious to a local lake association or the Department of Environmental Services. Support the Lake Host program, whether by volunteering at a launch or backing the funding that keeps inspectors stationed there. The science is clear that the cheapest, most effective moment to stop an invasive plant is before it ever gets established, and that moment depends on thousands of small acts of vigilance from the people who love these waters.
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