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Volunteers pitch in to clear Charles River of invasive weeds

The state had crews using mechanical harvesters to uproot invasive water chestnuts from the Charles River in Waltham last month.

Photos by Wendy Maeda/Globe Staff

The state had crews using mechanical harvesters to uproot invasive water chestnuts from the Charles River in Waltham last month.

Dovi Murray bought her house in Waltham 28 years ago mainly for the backyard, which lies just a few steps from the Charles River. She has fond memories of paddling through those waters with her young daughter, and taking the family’s canoe and small motorboat out for a spin on sunny days.

But in the past decade, Murray has been rendered boatless — not because of the expense, or because her daughter has grown up. She is simply tired of fighting the endless growth of weeds in the river behind her home.

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“The cove where we live is completely choked with water chestnuts,” Murray said last month, referring to how the plant’s wide leaves spread atop the water’s surface. “There would be no way to navigate a canoe in there with all the weeds, and they would just get caught in a motorboat’s propeller and ruin the engine. We can’t get out to enjoy the river, and it’s an eyesore.”

The Charles in recent years has been increasingly plagued with invasive aquatic weeds such as water chestnuts and milfoil, just like numerous other waterways throughout New England. And as many residents pull out kayaks and canoes for recreational use in the summer months, the state is funding the dispatch of mechanical harvesters to uproot the Charles River plants before their seeds spread.

“We need three to four good years of the machines to get it to the point where it’s manageable, so that all we’ll need is volunteers handpicking to keep the population low,” said Larry Smith, owner of Charles River Canoe and Kayak. As Smith stood on the shore near Charles River Road in Waltham last month, several of the human-operated harvesters clicked and clacked behind him on the water’s surface, methodically gathering water chestnut plants on a conveyer belt. Over an eight-hour shift, three machines can typically fill about two dumpsters with the weeds.

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The water chestnuts and milfoil — both stringy, leafy, and rapidly growing — have been clogging New England’s ponds, lakes, and waterways for decades. Both plants are native to parts of Asia and Europe, and were accidentally introduced here more than a century ago. Now, experts blame boats and birds for unknowingly spreading them to uninfested waterways.

The state has spent hundreds of thousands of dollars to fight the invasive flora, investing in the mechanical harvesters, and paying divers to suction them up with large vacuum tubes, and install barrier mats on the floors of some waterways to prevent new plants from sprouting.

8 hours of harvesting by 3 machines fills2 40-yard dumpsters with weeds

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Conservationists have also been urging volunteers to paddle out to problem areas and help handpick the weeds, throwing what they cull into shoreline dumpsters for composting.

Many seem to enjoy the hard work of pulling weeds from the muddy riverbed.

Karen Enriquez, volunteering as part of a service day for her company last month, sat with a friend, Patrick Keane, as they took a break from their weeding, clad in shorts, T-shirts, and heavy yellow gardening gloves. Their kayak was among about a dozen on the river in Waltham that day being used by volunteers working to rid a cove of its blanket of water chestnuts.

“It’s a beautiful day to be out on the Charles,” Keane said energetically, noting that environmental science has always piqued his interest. “It’s rewarding, and we get exercise from the paddling and pulling. It’s a good feeling to help and clean up.”

The water chestnut situation has become especially dire in the Charles River Lakes District, which spans about 200 acres in parts of Newton, Waltham, and Weston. Though local interest groups garnered state funding in the 1990s, and then again in 2006 and 2007, the plants grew out of control as money for the effort disappeared amid the financial crisis in 2008.

But as the economy regained its footing, so did the funding for weed eradication. Last year, the Legislature earmarked about $200,000 to fight water chestnuts in the Charles and Mystic rivers, and awarded tens of thousands of dollars more in matching grants for ponds and lakes around the state.

Smith estimates the Charles River needs several more summers of mechanical work and physical labor before the problem shrinks considerably. “This is about a $1 million project over about four years,” he said.

The state’s operating budget for this fiscal year includes $350,000 for aquatic weed control statewide, half of which will go toward the Charles River Lakes District. The Department of Conservation and Recreation’s capital budget also set aside $500,000 for restoring aquatic habitats, and a “significant portion” of that will go toward removing invasive weeds, according to Anne Carroll, director of the agency’s water resources office.

The funding is a key step forward for eradicating the pesky plants, conservationists say.

“Without these preventative measures, the Charles River Lakes District would basically become a swamp,” said Amy Rothe, a spokeswoman for the Weston-based Charles River Watershed Association.

Timing is also of the essence. Removing the plants in early summer, while their seeds are still attached, is considered to be essential to solving the problem. One water chestnut seed can carry 10 to 15 potential new plants, and each plant can produce up to 20 seeds, according to data from Columbia University.

“They multiply exponentially,” Rothe said. “We want to prevent these plants from spreading their seed, not just put a Band-Aid on the situation.”

Last year, the district saw about 500 volunteers handpicking the weeds, and the harvesting machines cleared about 10 acres of the river system in the beginning of the summer, she said.

The weeds also seem to love that dirty water. Storm run-off carrying pollutants like phosphorous into the river act as a super-fertilizer for the water chestnuts, spurring the growth of an already swiftly swelling species, said Michele Grzenda, Weston’s conservation administrator.

“The Charles River has twice as much phosphorous than what’s healthy for this river’s system,” Grzenda said. “It used to be a main ingredient in fertilizer. It’s what helps the plants grow.”

Some agencies have turned to using herbicides to control certain types of weeds, much to the chagrin of many local residents who worry that the chemicals could seep into the water supply.

The herbicides are not embraced in the Charles River Lakes District for a variety of reasons, Rothe said. “While herbicides can be used to treat milfoil, fanwort and algae, they haven’t been found effective on water chestnuts,” she said.

Rothe said the organization also generally stays away from the chemicals to stay sensitive to the potential pollutant issue, noting that it prefers a “more holistic method, like hand-pulling.

“Mechanical harvesting prevents the plant from coming back here every year,” she said. “Our goal is to use mechanical harvesters to remove dense vegetation, and then use volunteer hand-pullers as a post-management strategy.”

On an idyllic day last month on the Charles, mossy-green weeds blanketed entire stagnant coves, with some clusters the size of a football field. Even as Smith hosted a tour on his pontoon boat, the engine puttered out 15 minutes into the ride. He leaned over the boat’s stern to remove the culprit, weeds that had entangled the propeller, and revved the engine up again.

After the boat ride, Smith ticked off all the ways he and other conservationists were fighting the weeds. But he conceded that the invaders likely would never be fully wiped out, based on their reproductive abilities.

“It will probably always be here,” Smith said, sporting a wry smile. “Our goal is just to make it manageable.”

Jaclyn Reiss can be reached at jaclyn.reiss@globe.com. Follow her on Twitter: @JaclynReiss.
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