Blog - Charles River Watershed Association

Cyanobacteria bloom is a clear example of why we need environmental protections

Posted by Alexandra Ash

8/3/17 10:26 PM

There is currently a cyanobacteria outbreak in the Charles River, threatening the health of pets and interfering with folks' recreational plans. Based on field observations, the outbreak (or blooms) appears to be limited to the section of the river downstream of the Boston University Bridge. The Department of Conservation and Recreation urges the public to avoid contact with the water and to prevent pets from drinking it. 

cyanobacteria bloom

The cyanobacteria bloom in the Charles River near the Esplanade as seen on Monday, July 31, 2017.

Cyanobacteria, also known as blue-green algae, are photosynthetic bacteria that occur naturally in the Charles River. These organism can thrive in conditions other aquatic species may find inhospitable such as warm, stagnant water, commonly found in the Lower Charles River Basin in hot, dry summer months. Phosphorus pollution entering the Charles River in stormwater runoff feeds cyanbacteria allowing them to multiply far beyond any natural population levels and produce blooms. Cyanobacteria can produce toxins which are harmful to humans, dogs, and other mammals. High concentrations of cyanobacteria in the water may mean high toxin concentrations. A cyanobacteria bloom can last anywhere from two weeks to several months, especially if hot weather continues to fuel its growth and low river flows do not push the bloom out to the harbor. CRWA is currently flying yellow flags in this area to warn recreational river users about this threat. Sign up for regular water quality notifications from CRWA. DCR and the City of Cambridge will likely post signs along the river banks.


The toxins cyanobacteria produce can cause minor reactions such as rashes or eye irritations or have more severe implications such as damage to neurological systems or liver function. Consumption of high doses of cyanotoxins can be deadly. Cyanotoxin exposure through swimming in a pond is suspected in one human death in the U.S. and sadly is far too common in dog deaths.


Currently the Charles River contains twice as much phosphorus as the river can safely absorb. This causes overgrowth of cyanobacteria and other plants resulting in imbalances in the ecosystem. To prevent cyanobacteria blooms in the Charles River from threatening public health and disrupting recreation, we must prevent excessive phosphorus and other nutrients from entering the river via polluted stormwater.



A paddler enjoying a summer day in the Charles River near Cambridge. 

Climate change will only exacerbate the issue of cyanobacteria blooms in the Charles. Rising water temperatures will provide a cozy environment for cyanobacteria to thrive. Heavier storms will wash more phosphorus pollution into the Charles, pushing the ecosystem further out of balance. Longer periods of dry weather between rainstorms will contribute to lower flows and stagnant stretches of river. Together, these effects will likely cause more frequent toxic cyanobacteria blooms, impacting public health and closing the river to recreation. We need to act now to address these problems. 


The most direct way to prevent cyanobacteria blooms in the Charles River is to reduce the amount of phosphorus and thermal pollution entering the river by changing how we manage stormwater runoff. Instead of allowing clean rainwater to pick up contaminants as it rushes over paved surfaces into storm drains and into the river, communities and property owners can use rain gardens and other forms of green infrastructure to slow the water down, filter out pollutants and recharge it into the ground. This approach has the added benefit of replenishing groundwater levels and moderating the effects of both flood and drought. 


While we can each do our part to prevent phosphorus pollution, reducing phosphorus in the river to healthy levels will require coordinated and substantial efforts—the type of efforts made possible by smart policy and strong regulations. Unfortunately, neither the U.S. EPA nor Massachusetts Department of Environmental Protection is taking a leadership role on protecting clean water. Instead, U.S. EPA is systematically undermining protections for clean water.


Now is the time to address the underlying causes of these cyanobacteria blooms. It is not the time to weaken protections for clean water.  


CRWA is deeply concerned about efforts by the U.S. EPA to weaken the federal Clean Water Act. The day before the Massachusetts Municipal Stormwater Permit under the Clean Water Act was scheduled to take effect, EPA announced that it was delaying the permit for one year. This long overdue permit requires municipalities to better manage stormwater runoff to prevent it from entering rivers and streams. If implemented, this permit would help limit the severity and frequency of cyanobacteria blooms while helping communities adapt to climate change. In another attack on the Clean Water Act, the EPA proposes to repeal the Clean Water Rule that clarified protections for headwaters, seasonal streams and wetlands. Now is the time to address the underlying causes of cyanobacteria blooms. It is not the time to weaken protections for clean water.  


View current cyanobacteria advisories

Topics: U.S. EPA, Stormwater, Pollution, Charles River Pollution, Advocacy

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About Charles River Watershed Association:

One of the country's oldest watershed organizations, Charles River Watershed Association (CRWA) was formed in 1965 in response to public concern about the declining condition of the Charles. Since its earliest days of advocacy, CRWA has figured prominently in major clean-up and watershed protection efforts, working with government officials and citizen groups from 35 Massachusetts watershed towns from Hopkinton to Boston. Initiatives over the last fifty years have dramatically improved the quality of water in the watershed and fundamentally changed approaches to water resource management.