What is causing the ponds in Plymouth, MA to be closed?

Cyanobacteria, also known as blue-green algae, has reached unsafe levels in several ponds in Plymouth, Massachusetts, forcing the town to close the affected waterways.

How can the cyanobacteria in Plymouth's ponds affect people and pets?

The cyanobacteria can cause gastrointestinal illness, nausea, and diarrhea in humans, and can make pets, especially dogs, "very, very sick," according to the town's Public Health Director.

What is the town of Plymouth doing to address the cyanobacteria outbreak?

Plymouth has posted advisories warning the public to stay out of the contaminated ponds, and has banned all water activities, including boating and swimming, until the situation is resolved.

Home / Environment / Toxic Algae Outbreak Empties Plymouth, MA Ponds

Toxic Algae Outbreak Empties Plymouth, MA Ponds

5 Aug

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Summary

Several ponds in Plymouth, MA filled with dangerous cyanobacteria
Bacteria can cause gastrointestinal illness and harm pets
Town officials urge public to avoid all water activities in affected areas

Toxic Algae Outbreak Empties Plymouth, MA Ponds

As of August 6th, 2025, several popular ponds in Plymouth, Massachusetts have been completely emptied due to a dangerous cyanobacteria outbreak. Also known as blue-green algae, the bacteria have reached unsafe levels in at least six local waterways, including Billington Sea, Russell Mill Pond, and Great Herring Pond.

According to Plymouth's Public Health Director Karen Keane, the cyanobacteria bloom poses a serious health risk, potentially causing gastrointestinal illness, nausea, and diarrhea in humans. Pets are especially vulnerable, with Keane warning that the bacteria can make dogs "very, very sick."

In response, the town has posted advisories urging residents and visitors to stay out of the contaminated ponds. All water activities, including boating and swimming, have been banned until the situation is resolved. Local resident Rosemary Conlon expressed disappointment, noting that her grandchildren can no longer enjoy the ponds during the summer.

Town officials are closely monitoring the affected areas and advise the public to report any suspected cyanobacteria blooms to the local authorities. While the current outbreak has forced the closure of several popular recreational sites, there are still other ponds available for residents to enjoy the summer weather.

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