ASHFIELD – The Selectboard plans to vote on and fund a solution to remove invasive species from Ashfield Lake in fiscal year 2026.

Fanweed, also known as Cabomba caroliniana, is an invasive species native to the southern United States and Central and South America. Fanweed was first observed in Massachusetts in the 1890s, according to the United States Geological Survey (USGS), and was added to the state’s prohibited plant list on January 1, 2006. Fanweed can enter different bodies of water in a variety of ways, including water currents, boats, and birds.

The plant typically grows in waters less than 10 feet deep, according to the state Department of Conservation and Recreation. The competitive plant negatively impacts ecosystems by overgrowing natural vegetation and limiting space for fish and recreational use, according to Joe Onorato, co-founder of Water and Wetland. Water and Wetland is a South Grafton-based lake, pond and wetland management company.

The invasive species has been on the Selectboard’s radar for over a year, but the board has struggled to find funding for a solution. Volunteer hydrologist Drew Haerer of Ashfield has been monitoring the fanweed and proposing solutions to combat the problem.

The two main options Haerer presented to the Selectboard were purchasing a mechanical harvester to manually remove the fanweed or applying an annual herbicide treatment to control the fanweed. According to Town Manager Paul McLatchy III, both options are costly and have their pros and cons.

“With herbicide treatment, there is a strong community opposition to using herbicides of any kind in the lake, which is understandable. With mechanical harvesting, it’s much less invasive. There are no chemicals used or anything like that, but the city would have to buy some kind of harvester and then man it to have someone go around and literally pull out these invasive species. Either way, it’s difficult.”

The mechanical harvester would cost about $80,000 and someone would need to operate the machine to remove the common sedge. A herbicide treatment costs $45,000 and would need to be done multiple times every few years as needed. Neither solution will completely eradicate the common sedge. The selection committee expressed interest in the mechanical harvester because it would be a one-time purchase.

“It will take several years to treat anyway, and even after that, you’ll need smaller treatments throughout the year, so it will never go away completely,” McLatchy said. “It needs ongoing treatment, rather than a one-off treatment.”

During a meeting with the Selectboard last week, Haerer said the city should conduct a study of the lake before making any decisions about treatment. He recommended using available funds to study the lake’s invasive species in the fall and then coming back to discuss treatment.

“It’s hard because there is no good option,” Haerer said.

Haerer said consultants would likely recommend only the chemical treatment method. However, Selectboard members are skeptical that Town Meeting voters would approve the use of herbicides.

“I just can’t imagine the city agreeing to the use of fluoride in the lake,” said Selectboard Chairman Steven Gougeon, “regardless of what the science says.”

Last week’s discussions ended in an impasse without a solid solution being found. Ultimately, Selectboard members and Haerer agreed to continue researching mechanical harvesters and conducting a thorough study of Ashfield Lake.

Staff writer Madison Schofield contributed reporting.