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Consultants report limited invasive weeds at Foxborough reservoir; no lake-wide treatment recommended
Summary
Town consultants told the Conservation Commission that 2025 fluridone treatment largely controlled fanwort and variable milfoil; only a small area of active fanwort remains and targeted treatment was discussed, while algae testing found no toxic results and storm-drain sampling will continue.
Consultants reported to the Foxborough Conservation Commission on May 18 that a 2025 fluridone treatment produced strong control of fanwort and variable milfoil across the reservoir, leaving only a localized patch of active fanwort in the southwest corner that may merit targeted treatment in July.
Ken Wagner and Colin Goslin, who inspected the reservoir, said most invasive species were limited and that pond lilies and other plants were less abundant than in prior years. "The fluridone treatment of 2025 appears to have yielded a desirable level of control over fanwort and variable milfoil," the report states.
Commissioners reviewed algae test results and were told that, at the time of testing, no toxic algae was detected. Consultants recommended lowering the water level temporarily (removing dam boards) to move algal mats over the dam and reduce standing mats; the town implemented that measure earlier in the spring and monitored the change.
Sampling of storm-drain outfalls will continue, the commission was told, following detections of chlorinated solvents in a dry period last year. Staff notified state authorities; the state characterized the specific area as a culverted/storm-drain system and judged concentrations acceptable for that classification. Commission members flagged the drainage paths around the railroad corridor and an old phosphate facility as areas to watch.
The consultants recommended no lake-wide chemical treatment this year but suggested monitoring the small active fanwort site and considering a targeted diquat treatment in July only if recovery is evident. The commission accepted the consultants' recommendation and authorized continued monitoring and follow-up sampling of outfalls and hotspots.
Next steps: targeted monitoring and possible spot treatment in July if the southwest patch of fanwort regrows; ongoing storm-drain sampling and reporting to the commission.
