WORCESTER, MA — Residents planning to spend time at Coes Reservoir are being told to stay out of the water after testing found cyanobacteria at levels exceeding the state’s recreational public health threshold.
The City of Worcester announced Friday, Aug. 7, that Coes Reservoir is closed to recreational water use until further notice. Residents should not swim, boat or fish at the reservoir, and pets should also be kept out of the water.
The closure comes during the summer recreation season and while another Worcester lake, Indian Lake, remains under its own cyanobacteria health advisory.
Testing Leads to Coes Reservoir Closure
According to the City’s Department of Sustainability and Resilience, Worcester received testing results Aug. 7 showing cyanobacteria densities at Coes Reservoir above the state recreational threshold.
The dominant cyanobacteria identified in the testing were Aphanizomenon and Woronichinia. According to the City, both have the capacity to produce toxins.
Cyanobacteria occur naturally in water, but the City said high concentrations can be harmful to people and animals. Because of the testing results, the Massachusetts Department of Public Health advises that the reservoir remain closed until additional testing shows cyanobacteria densities have returned to safe levels.
The City has not provided a specific date for when Coes Reservoir could reopen.
Indian Lake Also Remains Under Advisory
Coes Reservoir is not the only Worcester recreational waterbody currently affected.
The City said Indian Lake remains under a health advisory because of cyanobacteria. Worcester officials plan to continue testing both Indian Lake and Coes Reservoir and will reopen each when testing determines conditions are safe.
For residents who regularly use Worcester’s lakes for swimming, fishing, boating or other outdoor recreation, the advisories mean activities involving contact with the water should be avoided at the affected locations until the City announces that restrictions have been lifted.
Other City Swimming and Water Recreation Options Remain Open
The closures do not apply to all Worcester recreational water facilities.
The City said Bell Pond beach remains open, along with Worcester’s municipal pools and spray parks.
Residents should continue checking the status of individual lakes before visiting because testing and public health conditions can change.
The City has not reported in the Aug. 7 announcement that anyone has become ill in connection with the cyanobacteria detected at Coes Reservoir.
What Happens Next
The Department of Sustainability and Resilience will continue testing Coes Reservoir and Indian Lake.
There is no predetermined reopening date for either affected lake. According to the City, each will reopen when additional testing determines cyanobacteria densities are at safe levels.
Residents can check lake conditions, advisories and other information through the City of Worcester’s Blue Space recreation and water quality information.
Questions about the closures can also be directed to the Worcester Department of Sustainability and Resilience at 508-799-8324.
🔎 W.U.W. Verification Box
• Project / Topic: Cyanobacteria closure at Coes Reservoir and continuing health advisory at Indian Lake.
• Current Status: Coes Reservoir is closed to recreational water use until further notice. Residents should stay out of the water, stop boating and fishing, and keep pets away from the water. Indian Lake also remains under a cyanobacteria health advisory.
• Key Dates or Decisions: On Aug. 7, 2026, Worcester received testing results showing cyanobacteria levels at Coes Reservoir above the state recreational public health threshold. The City announced the reservoir’s closure the same day.
• Estimated Cost: The City’s Aug. 7 announcement does not provide a cost associated with testing, monitoring or the closures.
• Timeline: Both Coes Reservoir and Indian Lake will continue to be tested. The City has not announced a specific reopening date for either waterbody.
• Immediate Next Steps: Worcester will continue cyanobacteria testing and will reopen each affected lake when testing determines conditions are safe.
• Primary Sources: City of Worcester Office of the City Manager and Department of Sustainability and Resilience, Aug. 7, 2026 public notice.
• What We Do Not Yet Know: The City has not provided a projected reopening date for Coes Reservoir or Indian Lake, and the Aug. 7 announcement does not report any confirmed illnesses associated with the cyanobacteria detected at Coes Reservoir.
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