City of Worcester, MA

WORCESTER, Mass. – Coes Reservoir is reopening following the receipt of test results confirming that cyanobacteria concentrations do not pose a threat to public health, however a temporary closure is planned for Monday, August 3 to allow for a preventative treatment.

On July 22, 2026, the municipality received cyanobacteria density testing results that exceeded the state recreational threshold and closed the reservoir to the public as a result. Since then, cell densities have declined, and there is currently no threat to public health. 

A preventative treatment is scheduled for Monday, August 3, which will require a temporary closure. The day of the treatment, the municipality advises that all persons stay out of the water, discontinue boat use and fishing, and keep pets out of the water. Water use restrictions will be lifted the following day.

Cyanobacteria are naturally occurring but can be harmful in high densities. The municipality has an active cyanobacteria monitoring and management program intended to keep our lakes safe for recreation and wildlife. To learn more about cyanobacteria and their toxins, please see our video series “The Blue Space Minute”, which can be accessed with this link: https://www.youtube.com/watch?v=1ZL9RMDapJc.

For questions, please call the Department of Sustainability and Resilience at 508-799-8324 or visit www.worcesterma.gov/BlueSpace.