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Coes Reservoir Closed Due to Cyanobacteria

For Immediate Release: 10/5/2022 12:10 pm

The Department of Inspectional Services has ordered the closing of Coes Reservoir because of the presence of cyanobacteria in densities that exceed the recreational 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 their pets out of the water until further notice. People and pets should avoid contact with scums.

Cyanobacteria are naturally occurring, but can be harmful in high densities. On 10/5/22, the City received cyanobacteria density testing results that exceeded the state recreational threshold. The dominant cyanobacterium present was identified as the genus Microcystis, which has the capacity to produce toxins. Because of this the Massachusetts Department of Public Health advises that the lake remains closed until further testing is conducted. The City will continue to test for both cyanobacteria and cyanotoxins, and reopen the lake when it is determined safe to do so.

If you or your pet has had contact with surface scums, wash off with freshwater immediately. If your pet has ingested any of the scums, contact your vet.

The City 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 refer to our educational video series “The Blue Space Minute”, which can be accessed with this link:

For questions, please call the Department of Sustainability and Resilience at 508-799-8325 or visit

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Worcester 311
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Phone: 311
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