Potentially toxic blue-green algae is turning portions of the Charles River green, causing state officials to warn people and pets to avoid contact with the water.
Potentially toxic blue-green algae is turning portions of the Charles River green, causing state officials to warn people and pets to avoid contact with the water.
courtesy of Julie Wood, Charles River Watershed Association

A sudden bloom of blue-green algae that has the potential to release toxins harmful to people and dogs has turned portions of the lower Charles River a scummy green several weeks earlier than in previous years.

People and pets should avoid contact with water that looks green and should not ingest it. Toxins that can be produced by the algae may cause skin rashes or stomach problems.

The type of algae measured in the river is called aphanizomenon, according to Julie Wood, a senior scientist with the Charles River Watershed Association, and can look like green paint spilled in the river, or strands of greenish silly string. On average, she said, there is one dog death a year in the state attributable to ingestion of blue-green algae.

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The bloom has been primarily spotted downstream of the MIT boathouse, and signs have been posted to warn boaters, dogwalkers, and people of the potential hazard.

Wood said that such blooms are unpredictable and poorly understood. They appear to be fueled by low river levels and warm weather, and the warm and dry spring may have created the right conditions for the bloom to occur in late June, rather than later in the summer as has been typical in years past.

“We really don’t know what causes the cyanobacteria blooms and why exactly we have them some years and not other years,” Wood said.

Predicting how long blooms will last is tricky. The last Charles River bloom, in 2010, lasted nearly two months, but they vary in length, Wood said. The current advisory will last for at least two weeks, because levels of the algae decline below a threshold for a certain period before it is safe, Wood said. She said she planned to take measurements Friday afternoon.

Wood said that testing is being carried out to determine whether the algae is secreting toxins. The blue-green algae are capable of producing a variety of toxins, but do not always produce them, and the factors that trigger their release are not well understood.

People who do come into contact with the water should wash any exposed body part.

“The river is not closed,” Wood said. “People should pretty much use their own discretion, avoid direct contact as much as possible, obviously avoid ingestion, which is a good idea anyway.”

To help the association monitor the bloom, people who see scummy water are being encouraged to take a photo, note the location, and e-mail the image to Julie Wood at jwood@crwa.org.