Summertime, and toxic algae is blooming: Here's what you need to know

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Blue-green algae, or cyanobacteria, blooms on the surface of the Charles River. (Jesse Costa/WBUR)
Blue-green algae, or cyanobacteria, blooms on the surface of the Charles River. (Jesse Costa/WBUR)

It's become an unfortunate rite of summer: the weather warms up and the algae breaks out.

Each summer, the Massachusetts Department of Public Health (DPH) posts alerts on harmful algae blooms in the state, warning people to keep themselves — and their pets — out of certain lakes, ponds and rivers.

Here's what you need to know to stay safe this summer:

Toxic algae? What's that?

Blue-green algae, or cyanobacteria, blooms in freshwater and produces a toxin that is harmful to humans. If you swim in affected water and swallow a lot of it, it can lead to stomach cramps and nausea, hay fever-like symptoms, or liver failure and death in extreme cases. Touching the water can also cause skin rashes.

What does it look like?

Sometimes it's a green scum on the water's surface, but it can also look like green paint, bright green strands or pea soup.

Green-blue algae blooms dot the surface of the Charles River along the esplanade by Community Boating. (Jesse Costa/WBUR)
Green-blue algae blooms dot the surface of the Charles River along the esplanade by Community Boating. (Jesse Costa/WBUR)

Is this the same thing as red tide?

No. "Red tide" occurs in saltwater and affects shellfish. In Massachusetts it's caused mainly by two organisms — Alexandrium and Pseudo-nitzschia — which produce toxin. When shellfish eat these organisms, the toxin accumulates in their bodies to levels that can be very dangerous for humans.

On the upside, it's generally safe to swim in the ocean during red tide outbreaks "because you just can't swallow enough of the algae to be dangerous," says Woods Hole Oceanographic Institution biologist and algae expert Don Anderson. He adds that the red tides we see in Massachusetts are less likely to cause respiratory problems, as happens in Florida.

Is it safe to swim in areas where there's blue-green algae?

No. "I would try to avoid it," says Anderson. "It can be dangerous, especially to young children who may swallow a lot of water."

Marc Nascarella, chief toxicologist for the Department of Public Health, goes further when speaking about the Charles generally: "Never really under any circumstances do we advise that individuals swim in the Charles River, because it is not routinely sampled for bacteria to evaluate its safety," he says.

Is it safe to go boating where there's blue-green algae?

Probably, if you stay out of the water. If you get splashed with algae-infected water, rinse it off as soon as possible, or you may get a rash.

How do you know if there's an algae bloom?

There's no statewide clearinghouse for blue-green algae blooms, so look for signs posted at specific lakes, ponds and rivers, or notices from towns. The state Department of Public Health will post advisories when it receives them, but the list is not always comprehensive.

Why are dogs always getting poisoned by blue-green algae?

When dogs swim in affected water, they often drink a lot of it, and also get algae in their fur and then lick it off, says Nascarella. So they can ingest a lot of toxin.

And here's another thing: Freshwater algae can wash up on the shores of the lakes, where it becomes a tempting snack for dogs. "It'll get all crunchy like potato chips, and the dogs love to eat that," says WHOI's Anderson. They can get very badly poisoned, he says, and even die.

Is drinking water in Massachusetts safe?

Nascarella says: "I'm not aware of harmful algal blooms that have impacted drinking water sources as of yet."

Will these toxic algae blooms get worse because of climate change?

Yup. Blue-green algae loves hot weather and nutrient-laden stormwater. So as the region sees more hot days and more heavy rainstorms, says Nascarella, "I think that harmful algal blooms will get more and more common."

Is there anything people can do to help prevent algae blooms?

Blue-green algae blooms are fed by nutrient runoff, especially phosphorus, says Emily Norton, executive director of the Charles River Watershed Association. She says people can help by avoiding fertilizer use on their lawns or by switching to electric vehicles. "There's actually phosphorus in the gasoline that drips onto the roads and gets into the stormwater runoff," she says.

Also: support green infrastructure like parks and rain gardens, which will also help mitigate the effects of climate change.

This article was originally published on July 26, 2019.

This segment aired on July 26, 2019.


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Barbara Moran Correspondent, Climate and Environment
Barbara Moran is a correspondent on WBUR’s environmental team.



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