City of Worcester, MA

WORCESTER, Mass. – The City of Worcester Department of Sustainability and Resilience has determined there is a presence of cyanobacteria at Coes Reservoir in densities that exceed the recreational public health threshold and therefore may contain toxins harmful to humans and pets. All persons should stay out of the water, discontinue boat use and fishing, and keep pets out of the water until further notice. 

Cyanobacteria are naturally occurring but can be harmful in high densities. On July 22, 2026, the municipality received cyanobacteria density testing results from Coes Reservoir that exceeded the state recreational threshold. The dominant cyanobacteria present were identified as the genus Aphanizomenon and the genus Woronichinia, which have the capacity to produce toxins. Due to these results, the Massachusetts Department of Public Health advises that the lake remains closed until further testing results show safe densities. The municipality will continue to test for cyanobacteria and will reopen the lake when it is determined safe to do so. 

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.