Consultants report limited invasive plants at Nepata Reservoir; no lakewide treatment recommended this year

Consultants briefed the Foxborough Conservation Commission on May 18 about monitoring and control efforts at Nepata Reservoir, reporting limited invasive-plant presence and recommending no lakewide chemical treatment this year.

Ken Wagner and Colin Goslin, the consultants who inspected the reservoir, said last year’s lakewide treatment achieved a low concentration of the herbicide across the lake and appeared effective against fanwort and variable milfoil. Their inspection this spring found only small, localized occurrences of those invasive species; water lilies were present but less abundant than in previous years. Algae samples taken during a period of dense algal presence did not show toxins at the time of testing.

To reduce algal mats, the town temporarily lowered the reservoir water level by removing two to three boards from the dam; the consultants said that measure, along with ongoing monitoring, should help flush algal material over the dam. The consultants noted they detected chlorinated solvents in a dry-period storm-drain sample; state staff classified the flow as a storm drain (not a perennial stream) and treated the concentration as acceptable for that conveyance, but the commission said it will sample again.

The consultants recommended targeted, localized approaches if regrowth is detected, including the possibility of treating a southwest corner pocket of fanwort with diquat (commonly called Diquat or product trade names such as Sonar) in July, rather than another lakewide application. They also noted boat-launch access and where people are launching remain community concerns. The commission accepted the report and asked staff to continue targeted monitoring, resample suspect drains, and report back to the commission.