WORCESTER — After another summer of water-quality problems forced closures and advisories at several city waterways, Worcester officials are being asked to find a long-term way to keep Coes Reservoir and Indian Lake open during the busiest months of the year.
Councilor-at-Large Gary Rosen filed an order during the Aug. 18 City Council meeting asking City Manager Eric Batista to provide recommendations for reducing recurring summer closures at the two recreational lakes.
The order passed the council and comes after repeated restrictions related to cyanobacteria, along with separate water-quality incidents at other Worcester waterways.
“There must be some way we can get these beaches under control so we don’t have to close them down during the months of July and August when they see the most use during summer vacation,” Rosen said.
Rosen suggested Worcester could work with Worcester Polytechnic Institute to study possible long-term solutions.
“It would be good if we can take some steps, and we have WPI always looking for projects,” Rosen said. “There’s two locations for them, I would think these would be good projects for the students over there.”
Coes Reservoir faces repeated closures
Coes Reservoir has experienced several cyanobacteria-related closures this summer after avoiding such a closure in 2025.
The city first closed the reservoir July 22 after testing showed cyanobacteria levels above the state’s recreational public health threshold.
Follow-up testing allowed the reservoir to reopen July 31. It was temporarily closed again Aug. 3 for a preventive treatment and placed under another public health closure Aug. 7 after testing once more showed elevated cyanobacteria levels.
Indian Lake was also under a cyanobacteria advisory during that period.
The city had already applied copper sulfate to Coes Reservoir and Indian Lake on July 6 as a preventive measure intended to control algae growth.
The contrast with 2025 is notable. Worcester’s water-quality report for that year found cyanobacteria concentrations increasing at Coes in July, but levels remained low after preventive treatment and the reservoir did not close because of a cyanobacteria bloom.
Coes has experienced much longer closures in the past. In 2022, the reservoir was closed for 78 days because of cyanobacteria blooms.
Why cyanobacteria can spread
Scientists say there is no single explanation for why one lake develops a cyanobacteria problem while another nearby waterway does not.
Pamela Weathers, a biology and biotechnology professor at Worcester Polytechnic Institute, said nitrogen and phosphorus entering waterways can provide nutrients that encourage cyanobacteria growth.
Runoff from lawns, for example, can carry fertilizer nutrients into a lake. Heavy rainfall can also overwhelm stormwater systems and transport additional nutrients into waterways.
“Cyanobacteria love that and along with heat and the water in which they live, it stimulates their growth and reproduction,” Weathers said.
Weather patterns may further complicate the problem.
Katie Liming, Worcester’s lakes and ponds coordinator, said changing temperatures and precipitation patterns, combined with increased urban development, can increase the amount of nutrients entering waterways.
Periods of drought followed by intense rainfall can contribute to erosion and runoff, she said.
Weathers noted that warmer average summer temperatures could also encourage more cyanobacterial growth when sufficient nutrients are present.
Indian Lake also affected
Indian Lake exceeded the state’s recreational cyanobacteria threshold in early August, prompting the city to close the lake Aug. 4.
Testing identified several types of cyanobacteria, including Microcystis, Planktolyngbya and Aphanocapsa, which have the potential to produce toxins.
Massachusetts uses cyanobacteria cell counts as one measure in determining whether a recreational public health advisory is warranted. One threshold cited by the city is more than 70,000 cells per milliliter.
Residents also receive information from the Worcester Cyanobacteria Monitoring Collaborative, a volunteer group that samples waterways in Worcester and surrounding communities.
The collaborative’s Aug. 3 results rated potential cyanotoxin exposure risk as High at Indian Lake’s Clason Beach and Elevated at Coes Reservoir and Salisbury Pond.
City officials emphasize that the volunteer monitoring is not a substitute for official public health testing.
Liming said residents should follow city health advisories when they are issued and avoid recreation in affected areas.
Not every closure was caused by cyanobacteria
Worcester’s water-quality problems this summer have not all had the same cause.
Smith Pond Beach was temporarily closed after testing detected elevated levels of E. coli. The beach later reopened after subsequent testing produced acceptable results.
Lake Quinsigamond faced a separate issue in July when a sanitary sewer overflow led to temporary swimming and fishing restrictions in part of the lake. Those restrictions were lifted July 28 following additional testing.
The different incidents underscore the variety of factors that can affect Worcester’s urban waterways.
City already working on broader water-quality plan
Worcester’s Lakes and Ponds Program already monitors local water quality and works on projects designed to reduce nutrient pollution before it reaches waterways.
The city is also developing Project Blue Worcester, an initiative intended to establish water-quality targets for phosphorus, bacteria and dissolved oxygen and identify ways to reduce pollution, including potential stormwater improvements.
Rosen’s latest order puts a more immediate focus on keeping Coes Reservoir and Indian Lake available for recreation during the summer.
The city administration is now being asked to identify long-term measures that could reduce the recurring closures rather than relying primarily on seasonal treatments and short-term responses.
