You can rip them out, poison them, vacuum them up, or smother them with sheets of plastic, but the chances of eradicating the exotic plants that are invading the region’s ponds and lakes are slim, according to environmental officials.
“Once they are in your lake, you are very unlikely to get rid of them,” said Anne Carroll, director of the Office of Water Resources in the Massachusetts Department of Conservation and Recreation. “You just have to deal with them — like mowing your lawn.”
About a third of the approximately 3,000 freshwater lakes and ponds in the state are affected, according to Tom Flannery, who runs the department’s Weed Watchers program that trains people to spot and report invasive freshwater plants.
Lake Cochituate, which spreads across Natick, Wayland, and Framingham, is battling milfoil. Whitehall Reservoir in Hopkinton is covered with fanwort and milfoil. And parts of the Charles River’s lakes district — between Newton and Waltham — are so choked with water chestnut that the fanwort weeds underneath are barely visible.
“These invasives are called invasives for a reason,” Flannery said. “You can take a crystal-clear water body and introduce’’ an invasive plant, he said, “and literally the entire lake is covered top to bottom with weeds. You can’t fish, you can’t boat, you can’t swim, the wildlife suffers.’’
How long the process takes can vary, Flannery said, “depending on things like lake chemistry and depth, but I’ve seen a lake go from zero to 40 acres in one growing season.”
That does not mean it is time to give up the fight, though, both Carroll and Flannery said.
“It still makes sense to find things early and have a chance to save the lake,” Flannery said. “Even if you have a lake chock full of invasives, you haven’t lost the battle. The key is management. You have to work at it year after year — and spend a lot of money.”
He said the state spends about $500,000 annually on the battle, and municipalities and private associations spend about $1.5 million more. The state’s budget for the current fiscal year earmarks another $700,000 , Carroll said.
While Flannery said the figure is not close to what is needed, both he and Carroll are encouraged by a new state law that requires the Department of Conservation and Recreation to write rules to combat the spread of invasive species, and impose penalties for those who fail to comply. The regulations should be finished by the end of the summer, and will focus on requiring people to clean their boats, Carroll said.
“It’s pretty basic,” she said. “When you come out of a lake with invasives, look at your boat, at the motor, props, the trailer. A quick visual check should take care of it. Or run it through a car wash, or let it dry. We also ask people to empty out anything they filled with pond water and dump it on the ground far enough away that it won’t get back in.
“It’s not onerous, and it is now the law,” Carroll said. “There certainly are people out there who feel fatalistic about this problem, but we’re not. . . I think we’re keeping up.”
One source of optimism is Natick’s Fiske Pond , which flows into Lake Cochituate, she said.
In 2008, the shallow 67-acre pond was completely overrun with invasive plants, but especially with water chestnut, according to Flannery. The plant forms thick, fluffy green mats on top of freshwater bodies and chokes out all other vegetation. In a single season, an acre of water chestnut can produce enough seeds to cover 100 acres of water the following year.
But water chestnut also is relatively easy to yank up, and the state has spent close to $500,000 since 2008 on a removal program that not only has cleared Fiske Pond, but, more importantly, protected the more widely used Lake Cochituate, Flannery said. He said the amount of water chestnut taken from the pond went from 225 tons the first year to only about “a dumpster load” this summer.
“It’s a pretty good success story,” he said. “We started with big mechanical harvesters and we are now at a point where we are able to control it with just volunteers hand-pulling from kayaks.”
By contrast, Whitehall Reservoir, a 575-acre pond in Hopkinton, is completely taken over by fanwort and milfoil, Flannery said.
“In the spring and early in the summer it’s boatable,” he said, “and with a canoe or a kayak there are still a few little channels where you can sneak through the weeds. But right now, most fishermen give up on that lake.”
No one has given up on the lakes district of the Charles River, where scores of volunteers meet regularly at the dock of Charles River Canoe and Kayak in Newton for forays to pull up water chestnut. The weed, which covers about 50 acres of water between the Moody Street Dam in Waltham and Commonwealth Avenue in Newton, impedes recreation and kills fish and native vegetation, according to Julie Wood, a scientist with the Charles River Watershed Association .
“Our main goal is to keep recreational access open and to keep this infestation contained,” Wood said. “From what we can tell, the spread is not getting too far ahead of us, and we may even be making some headway on reducing the overall amount of cover.”
She said her organization has raised about $20,000, and asked the state to help fund a more aggressive program using mechanical harvesters.
Various approaches have been used to fight the invasive weeds in Lake Cochituate, which comprises three ponds — South, Middle, and North — and covers more than 600 acres. The state found milfoil in South Pond about 10 years ago, and proposed a herbicide treatment there and in Middle Pond, but Natick opposed the plan for fear the chemical would contaminate nearby wells, according to the DCR’s Carroll.
Herbicides were used, however, in North Pond in Wayland and “it was stunningly successful,” she said. “All the native plants were still there and the fish, but every scrap of milfoil was gone.”
Meanwhile, the state worked with Natick and local environmental groups on a nonchemical approach in Cochituate’s Middle and South ponds, hiring divers to suction up the weed with an underwater vacuum in a 5-acre area around the state beach and boat ramp. The work was expensive and so slow, Carroll said, that by the time an acre of weeds was cleared, another acre had grown in its place.
“We did it for two years and found we were just treading water, so this year we allowed chemical treatment in that location and it’s been very successful,” said Natick’s conservation agent, Bob Bois.
He said numerous groups also pooled money to buy benthic matting to lay on the lake bottom and smother the milfoil plants, which worked, but only in small areas.
“I think we’ve got to the point where even though these other options work, they’re not long term,” Bois said. “We need to rethink the overall weed management plan for the lake.”
“The problem is quite prevalent in lakes and ponds all over the state,” Carroll said, adding that steps to educate the public about the invasive plants are essential.
Another priority is to make sure that the weeds stay out of uncontaminated waterways — such as Walden Pond in Concord.