NORTH SWANZEY — Keene City Councilor Bobby Williams was chest-deep in muddy water. N.H. Rep. Sparky Von Plinksy was yanking at vegetation with a rake. Vernon Thornblad lost a rubber boot to the muck, and Jamie Doherty said she’ll never be able to wear her socks again.

So passed a mild Tuesday evening near Dillant-Hopkins Airport.

Wading amongst frogs and cattails, the four-person crew was tackling a water chestnut patch just a stone’s throw from the road. It’s the latest small gathering organized by Williams to remove invasive species in and around Keene.

A few years ago, Williams, who also serves on the Keene Conservation Commission, took a course with the N.H. Invasives Academy through UNH Cooperative Extension. He’s “had a bee in [his] bonnet” ever since. The conservation commission has been talking about taking on invasive species for about a year, and this summer they decided to take action, Williams said.

Von Plinsky, the commission’s chairman, explained that invasive species can choke out native species, eliminating food sources for certain insects and other animals while disrupting the greater ecosystem.

According to the National Invasive Species Information Center, water chestnut is native to Eurasia and Africa, and was brought to the U.S. in the 1870s for ornamental purposes. It has long roots, and the fan-shaped leaves form rosettes, radiating outward from a center stem. Collectively, these rosettes form a thick mat of greenery at the water’s surface.

Eloise Clark, vice chair of the conservation commission, was the one who first noticed the patch of water chestnut near Airport Road. Williams said this patch is the only one he knows of in the area, but it was important to remove it before it goes to seed — which it typically does in mid-July — and spreads farther across the wetland.

In May, Williams organized Garlic Mustard Pull Challenges to remove garlic mustard near Beaver Street in Keene. The invasive plant grows on land and has leaves that smell like garlic when crushed.

“There are significant effects on ecosystems beyond just taking up space,” Williams said. Garlic mustard — which was brought from Europe more than 150 years ago for food and medicinal uses — can actually change the soil it grows in, making it uninhabitable for other species.

Doherty, a volunteer helping remove water chestnut Tuesday evening, also participated in one of the garlic mustard pulls. She said the group wiped out a large swath of the plant in just an hour and a half. It can be an enjoyable endeavor, she added, especially as a break from her work as a web developer.

“You’re doing good, but you’re also blowing off steam,” she said.

Garlic mustard and water chestnut are easy enough to remove with simple tools and bare hands, Williams said, but other species like Norway maples and Japanese knotweed would require more manpower and advanced methods.

“I would love to get a group of regulars together,” Williams said, and he hopes to take what he’s learned from this summer and create a more formalized program in the future.

Von Plinsky admitted that given how omnipresent invasive species are, it can be overwhelming to think about trying to tackle everything.

“It’s about identifying what we can do with the resources we have,” Von Plinsky said. “You have to pick your battles.”

There are several invasive species across Keene, including Norway maples, Japanese knotweed, burning bush and bittersweet vines. Thornblad said he even has invasive bamboo in his yard.

Invasive species have many different ways of spreading to new regions, according to the National Invasive Species Information Center. Like water chestnut, many species are planted for decoration. However, some invasive plants are spread by humans unintentionally, such as when seeds are stuck to the hull of boats or a hiker’s backpack.

Williams said the conservation commission and volunteers can work on addressing the invasive species that grow in public spaces, but he wants to get the word out to private landowners too. He recommended that people interested in learning more about invasive species — and potentially addressing the problem in their own backyards — start with UNH Extension’s online resources.

Invasive species can’t be composted, as this could result in the seeds spreading even farther, so the plants are put in garbage bags to decompose. The uprooted water chestnut just needs to be kept away from water, Williams said, but the garlic mustard had to sit in bags for a month before the conservation commission felt it could be discarded without seeds taking root.

Just down the road from the airport, the crew moved methodically, using rakes and bare hands to pull up tendrils of water chestnut. The waterlogged leaves were loaded onto a boat, brought back to the bank, and then dumped to dry out on the grass. The muddy tangle of discarded roots and leaves continued to spread along the road, and after an hour of work the team had made a noticeable dent in the patch.

Williams said he’s not sure which invasive species he’ll try to take on next, but he’s still learning as he goes.

One lesson from Tuesday? What gear might be helpful in the future.

“I’ll be asking for waders for Christmas,” he said.

Molly Bolan can be reached at 352-1234, extension 1436 or mbolan@keenesentinel.com. Follow her on Twitter @BolanMolly.