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Massachusetts Water Resources Authority


September 4, 2019


Sean Navin, (617) 788-1112

Metallic-Tasting Algae in Reservoirs

Starting in late August, an algae bloom began to occur in the Wachusett reservoir. While the presence of low levels of algae (naturally occurring microscopic plants) is a sign of a healthy reservoir, from time to time, one species may increase or bloom in greater numbers. This particular bloom consists of Chrysosphaerella, a golden brown algae, which can leave a metallic taste to tap water that may be noticeable to some customers.  While this algae bloom may present a nuisance taste and odor condition, the water remains safe to drink.

MWRA’s ozone disinfection is normally very effective at removing these types of tastes, and MWRA increased the ozone dose at the John Carroll Water Treatment on August 30th. The bloom is being monitored by Department of Conservation and Recreation (DCR) and MWRA three days per week.   Staff are collecting samples in the reservoir, performing microscopic analyses, and identifying and counting the algae concentrations.  In addition, water quality is monitored continuously with on-line analyzers immediately before and after treatment at the Carroll Water Treatment Facility, as well as further downstream. 

If you notice an off-taste, chilling water in the refrigerator and/or adding lemon is the easiest way to improve the taste.

A similar bloom is also occurring at the Quabbin Reservoir. The last bloom causing taste complaints in the Metro Boston area occurred in 2004 before the Carroll Water Treatment Plant went online.   

More information about the Wachusett Reservoir and water quality is available at If you notice a metallic taste, you can contact MWRA at 617-242-5323.    


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Updated September 4, 2019