Rosemary Lake Experiencing Algal Bloom
August 27, 2026
• Bright green algae in Rosemary Lake could be cyanobacteria, which can cause people and animals to get sick.
Earlier this summer, the town was warned about potentially harmful algae along the Charles River, which was present in areas close to Newton and Dedham. While that advisory had been lifted early last week, another alert was issued this past Wednesday, this time regarding Rosemary Lake, a center for summer recreation in the town.
While the town has not confirmed whether the lake was affected by cyanobacteria, they posted signs asking residents to limit their use of the site out of an abundance of caution. We spoke with the Needham Health Department, who issued the alert alongside the Park and Recreation Department.
