Zebra Mussels Found in Pittsfield's Onota Lake
PITTSFIELD, Mass. — The city will treat one acre of Onota Lake for zebra mussels.
On Wednesday, during a special virtual meeting, the Conservation Commission approved a series of three treatments with EarthTec QZ. During dive monitoring in August, a live adult zebra mussel was found near the boat ramp.
Parks, Open Space, and Natural Resources Manager James McGrath said it will begin in the next 7-10 days, and that this treatment is nearly identical to that in the fall of 2024, as approved by the ConCom and other entities.
EarthTec QZ, an EPA-registered liquid molluscicide, will be applied to a 1-acre section from a boat with GPS guidance, about 14 days apart. There will be signs and notices of treatments to alert the public.
Karen Murray, of the Lake Onota Preservation Association, explained that the area is from the rocky point north of the boat launch to the boat launch, and a little south of the fishing pier.
"Again, does that mean we have live zebra mussels? We don't know, but it's pretty strong evidence of a potential problem," she said.
Over the last few years, Pittsfield has grappled with occasional findings of the invasive species.
Pittsfield and LOPA embarked on an early detection process at Onota Lake in the fall of 2023; the state Department of Conservation and Recreation had found the area near the boat launch positive for zebra mussel eDNA.
Murray explained that they are using a parsimonious strategy, recognizing that eDNA detection in a waterbody is a signal that there could be a problem, but not clear evidence of early colonization because it could be from dead material. Divers are sent down to confirm the presence of zebra mussels.
In May 2024, divers found several empty shells but no live zebra mussels; a couple of months later, one was found south of the fishing pier along the shore and another near the rocky point north of the boat ramp, Murray said.
"So now we had confirmation in 2024 of zebra mussel likely early colonization, and that individual was fairly large, so it was probably there for a couple of years," she explained.
"There was treatment following that with EarthTech QZ."
Sampling done in 2025 was negative, but August testing came back positive for zebra mussel eDNA in three transects in the boat launch area. A diver then found a single live, "pretty good-sized" zebra mussel in 15 feet of water between the boat launch and that rocky point.
Solitude Lake Management was chosen as the vendor through a procurement process.
Zebra mussels are invasive freshwater mollusks that present a variety of ecological, recreational, and economic concerns.
In 2009, they were detected in Laurel Lake and its outflow in the Housatonic River in Lee/Lenox, and since then, the city has worked with the state Department of Conservation and Recreation to proactively monitor and bring awareness to proper boating care to help prevent the spread from one waterbody to another.
McGrath said he will try to secure some state funds for this effort, "because this is a big deal," and he would like to see a greater level of support from them.
Tags: conservation commission, onota, zebra mussels,
