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Blue-Green Algae in the Charles River

Amy Rothe, Director of Communications, Charles River Watershed Association

Have you noticed a green scum while on the Charles River in the last few months? Or perhaps you have read about the recent blue-green algae bloom advisories in the news? This summer, the Charles witnessed several blue-green algae blooms, from Newton down to the Charles River locks. Also known as cyanobacteria, blue-green algae are actually aquatic bacteria that, like algae, produce their own food through photosynthesis. Prolific growths of one or more types of cyanobacteria, or blooms, are typically observed in the Charles when water temperatures rise and river-flow falls. The Charles River has long suffered from excessive amounts of phosphorus, which enters the river through polluted stormwater runoff. The phosphorus acts as a fertilizer for the river: it feeds the cyanobacteria and causes it to grow in abundance. Additionally, the photosynthetic cyanobacteria thrive in warm water, and temperatures this summer have been some of the warmest on record. Charles River Watershed Association has had an active cyanobacteria monitoring program in effect since 2006, and this year is the first time we have observed a bloom in Newton.

When blue-green algae die, they release toxins that may be harmful to humans and animals. The Center for Disease Control and Prevention advises that contact with high levels of cyanobacteria has been found to contribute to eye, ear and skin irritation, and ingestion may lead to more serious health effects. Dogs that drink river water during a blue-green algae bloom are also highly susceptible to adverse reactions, and, in some cases, ingestion may lead to death.

Public health risks are not the only concern, however: blooms of cyanobacteria and other vegetation also can contribute to larger environmental problems. Large blooms can prevent sunlight from reaching submerged aquatic vegetation below. When a large mass of aquatic life (like blue-green algae and invasive species) dies, decomposition can deplete the river of valuable dissolved oxygen, which fish, mollusks and other aquatic animals rely on to survive. Extreme dips in dissolved oxygen levels may result in fish kills. All in all, the presence of blue-green algae can have a profound impact on the river’s health and ability to sustain life.

Phosphorus is present in many items that you may use at home, so there are many ways you can help reduce the amount of phosphorus entering the Charles. Test your soil to see if it actually requires any additional nutrients in the form of fertilizers, as many local soils do not. Most fertilizers contain phosphorus as a major ingredient, so if you do require additional nutrients, consider composting instead. Car exhaust also contains phosphorus, and this is deposited on driveways, streets and parking lots. Consider walking, biking or taking the T to nearby destinations instead. Also, be sure to pick up after your dogs and properly dispose of all waste in the garbage or pet waste composter. You can also help by reducing and treating stormwater runoff from your property through the use of rain gardens, rain barrels and permeable pavers.

Reducing stormwater runoff pollution not only leads to a healthier Charles but to an economically viable region as well. Larry Smith, the owner of Charles River Canoe and Kayak, states, “Our business depends on a healthy Charles, and we continue to grow and thrive as the water becomes cleaner.”

The Charles River Watershed Association’s (CRWA) programs address the root causes of blue-green algae blooms. CRWA works to eliminate phosphorus from entering the river and to decrease stormwater runoff by encouraging and implementing green infrastructure development (GI), which captures and cleans water where it lands instead of funneling it off to the river. For more information on CRWA’s GI projects or bluegreen algae in the Charles, please visit

September 2012

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