Which Mass. beaches have dangerous bacteria levels? New tool tracks data.

Local News

As large amounts of bacteria close Massachusetts beaches to swimmers, the state released a new interactive tool to monitor the information.

A lifeguard patrols the beach at Houghton’s Pond on July 20, 2023, where swimming was closed due to high levels of bacteria. John Tlumacki/Boston Globe

Massachusetts has some of the best beaches around, but this summer residents looking to hit their favorite swimming spots have been frequently thwarted by dangerous levels of bacteria or algae in the water. State officials conduct regular water quality tests at all Massachusetts beaches, issuing temporary swimming bans when necessary. 

As this summer’s heavy rains have led to a large number of water closures, the state is now providing a powerful new tool to track water quality from the Cape to the Berkshires. 

The Department of Public Health’s new interactive beach water quality dashboard improves access to this information on a number of levels. For starters, it is updated more frequently than the previous system, with new data being posted daily at 9:30 a.m. and 12:30 p.m.

It also offers an interactive map, clearly showing green dots for beaches open to swimming and red dots for those with poor water quality. States like New Hampshire have already made interactive maps like this available to the public. 

The map can be searched by town or by beach. Users can drag their mouse to select large swathes of the state to see data for, or hover over individual beaches to see their names, town locations, closure statuses, and water types. 

Finally, the new dashboard offers a section where users can see the results of recent water quality tests for any beach. This data seems to stretch back a few months, depending on which beach is selected and how often it is tested. Historical beach data can be found elsewhere on DPH’s website. 

A new interactive map from the Massachusetts Department of Public Health shows swimming bans as of Aug. 4, 2023. – Massachusetts Department of Public Health

As of Friday morning, 50 beaches were closed to swimming due to water quality issues. More than 1,100 public and semi-public beaches in Massachusetts are monitored. The frequency of this testing varies by beach and is determined by how likely a beach is to have poor water quality. Even if dangerous water is detected, these beach closures only amount to swimming bans. The beaches remain open for non-water recreation. 

The state can issue swimming bans for a variety of reasons but by far the most common is “bacterial exceedance.” This occurs when levels of bacteria, Enterococci or E. coli, exceed certain limits.

Enterococci and E. coli are known as “indicator organisms,” because they are used to predict the amount of pathogens in the water. Pathogens, which make people sick, are hard to measure directly in water, according to DPH. 

Bacteria can get into the water a number of ways, such as from stormwater run-off, sewer overflows, or malfunctioning septic systems. It can cause various issues in swimmers’ gastrointestinal systems, on their skin, in their eyes and ears, or in their throat and lungs. 

Although most swimming bans in Massachusetts are put in place due to large amounts of bacteria, a sizable chunk of closures frequently occur due to harmful algae blooms.

Cyanobacteria, or blue-green algae, occurs naturally. If certain conditions are met, it can multiply rapidly and infuse water with toxins. Exposure can cause illness in humans and has been known to result in the deaths of pets.


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