06/30/2026
We have been spared this problem over the years, but conditions this season could present a challenge.
Alex Woodle
EDITORIAL
Green menace: Toxic blooms are shuttering Massachusetts lakes and ponds
By treating water and preventing algae-causing pollution from reaching bodies of water, municipalities can limit the number of swimming days lost.
Cyanobacteria bloom warning signs at Crystal Lake in Newton. The algae is toxic to humans and deadly to dogs.
Cyanobacteria bloom warning signs at Crystal Lake in Newton. The algae is toxic to humans and deadly to dogs.
The bright green algal bloom that’s taken over President Trump’s remodel of the Lincoln Memorial Reflecting Pool may be embarrassing to the president, but it appears harmless to people and animals at present.
In Massachusetts, however, it’s a different tale. Dozens of ponds, lakes, and beaches have been hit by cyanobacterial harmful algal blooms and bacteria outbreaks, forcing shutdowns and putting a damper on summer fun.
Cyanobacterial harmful agal blooms look like light green or blue-green spilled paint, or surface scum, floating in the water. Exposure to toxins released by cyanobacteria, commonly known as blue-green algae, can be dangerous to people and pets, leading to nausea, diarrhea, asthma-like symptoms, or rashes. Ingestion of toxins can lead to liver or neurological harm. There have also been dog fatalities from drinking polluted water in Massachusetts. (Bodies of water may also be closed when high levels of E. coli are detected, indicating the possible presence of pathogens that can cause illness.)
It’s a problem that’s gotten worse across the globe in recent summers, a worldwide concern largely beyond the control of any local government agencies. Still, some cities and towns are taking promising proactive steps to minimize blooms and keep ponds and lakes open more often by treating water and preventing algae-causing pollution from reaching susceptible areas.
Harmful algal blooms are more likely to grow in warm, shallow, and still and slow-moving water that contains excess nutrients to help microorganisms grow. These nutrients, including nitrogen and phosphorus, can come from fertilizers, sewage, or heavy rain runoff.
Climate change is also contributing to more frequent, longer-lasting, and in some cases more intense blooms, which scientists predict will be exacerbated in the future. The Charles River has seen harmful algal blooms almost every summer for the past decade, with one lasting 12 weeks in 2020.
But consider what’s happening in Newton, a city determined not to suffer that fate at Crystal Lake, a 33-acre, roughly one-mile circumference kettle pond. It’s used for swimming, fishing, floating on rafts, and kayaking. It employs young lifeguards. And it draws big crowds in summer, offering an urban oasis just yards from the Green Line rumbling along the lake’s southern edge.
Harmful algal blooms had become more pronounced there in recent years, so the city addressed the problem in 2020 by adding an alum (aluminum sulfate) treatment, which binds phosphorous loads to the lake bottom. This process has been used successfully across New England, limiting blooms for five to 15 years.
Despite Newton’s efforts, on Monday, June 22, Crystal Lake was closed due to a confirmed cyanobacterial outbreak in one cove. Across the state, a handful of bodies of water have also already been temporarily shut down this summer after positive lab tests, including ponds on Cape Cod, Nantucket, and Martha’s Vineyard.
The hope in Newton is that with proactive efforts, the harmful algal bloom will at least be short-lived.
Preparing Crystal Lake cost $182,500, which incorporated three years of treatments as well as ongoing monitoring and scientific reports. Newton also acquired a $100,000 grant from the state to retrofit nearby underwater stormwater infrastructure to pretreat runoff that goes into the lake.
“The cost of treatment is a real issue for many communities,” Jonathan Yeo, Newton’s stormwater program planner told the Globe’s editorial board. “There is not a systematic state grant program to cover the costs. Newton is one of few communities to have a separate stormwater fund to cover costs for projects.”
Newton’s funding comes from a stormwater fee added to household water and sewer bills, an idea that’s catching on — 10 communities across the state, including Boston, have now adopted or are adopting the practice.
Scientists believe the most recent bloom in Newton was driven by warmer water temperatures, then high winds pushing organic material — which can include tree pollen, decayed leaves, pet waste, goose p**p, road runoff, and garden and lawn fertilizers — into the watershed that feeds Crystal Lake.
Those are factors that municipalities — and their residents — can control a lot more directly than climate change.
Soni M. Pradhanang, who researches water management at the University of Rhode Island, told the editorial board that using less fertilizer, keeping pet waste out of storm drains, maintaining septic systems, and avoiding unnecessary disturbance of shoreline vegetation can help.
“Those steps may seem small, but they add up when many households do them consistently,” Pradhanang said.
As for duration, blooms can last a week or months. Pradhanang said it depends on weather and nutrient levels. Aggressive actions for quick results like adding algaecides have been used on rare occasions as a last line of defense in places like Andover and Yarmouth, but the practice is controversial because wildlife can be harmed — cyanobacteria can release toxins in a burst when they die off quickly. But what generally happens is once a bloom has started, communities just wait for the conditions feeding it to diminish.
The Massachusetts Department of Public Health recommends reopening a body of water when two consecutive tests, one week apart, fall within the recommended guidelines. In Newton, a sample taken on June 24 was within normal limits. A second sample will be taken on Wednesday.
If it’s negative, the lake will reopen — just in time for a heat wave and the holiday weekend.
