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‘It Has Really, Really Spread’ — Green Algae Returns To Casco Bay

Susan Sharon
Maine Public
Casco Baykeeper Ivy Frignoca checks an algae bloom in Mill Cove, South Portland on Thursday.

It’s back — the unwelcome bright green slime that showed up around Casco Bay in several locations during the drought last summer has returned with a vengeance, and this year it has arrived even earlier.

The environmental group Friends of Casco Bay is actively monitoring the situation, and is worried about what algal blooms like these say about the health of the bay.

This story is the latest installment in our occasional series “Beyond 350: Confronting Climate Change.”


With climate change and an excess of nitrogen from stormwater and wastewater runoff, algal blooms are becoming more common around the world. Common and concerning, says Casco Baykeeper Ivy Frignoca.

“This breaks my heart. This is so extensive. We were just here a week ago and the bloom was just beginning and it has really, really spread,” she says.

Wearing thigh-high rubber boots, Frignoca is standing behind the Hannaford in South Portland’s Mill Cove, where what looks like a soggy layer of AstroTurf has settled over the mudflats, using up oxygen and suffocating everything underneath it.

Researcher Mike Doan says clams can be especially vulnerable.

“Last year we were seeing clams that were certainly having trouble — necks out at low tide, lying on the surface and eventually finding more and more dead clams,” he says.

Credit Susan Sharon / Maine Public
Maine Public
Green slime in Mill Cove in South Portland.

So far, no dead clams are showing up. But the Friends of Casco Bay have only just begun their monitoring.

They had hoped last year’s outbreak was an anomaly, caused by a combination of excess nitrogen and an extended drought, lots of sun and little rain. But this spring there has been more rain, the water is a little bit colder and still the slime is thriving.

After measuring the acidity of the mud in and around the algae, the team heads back to their office, where intern Emily Haggett has collected a DNA sample of the slime that has also showed up in Portland’s Back Cove and in Pleasantdale Cove in South Portland.

“We know it’s a green algae and we suspect that it’s the genus Ulva, sea lettuce. We don’t know what species it is,” she says.

Credit Susan Sharon / Maine Public
Maine Public
Green slime in Mill Cove in South Portland.

Haggett will send a DNA extraction to a lab to be sequenced. But however it is ultimately identified, no one is happy about its arrival or the thought of it becoming a trend. Casco Bay is one of the fastest warming bodies of water in the world.

“That’s my concern is water temperatures get warmer and warmer. We’re going to see more of this type of thing, episodes where you might think of them as more common to our south now become more common here as the temperatures warm,” Doan says.

In other water bodies, harmful algal blooms have sometimes been the precursor to “dead zones” — oxygen-depleted areas where marine life can no longer survive. Frignoca says her goal as Casco baykeeper is to take action before the bay is seriously impaired.

Credit Susan Sharon / Maine Public
Maine Public
Friends of Casco Bay out on mudflat in Mill Cove in South Portland.

She says there ways for others to help.

“We’ve got to stop using lawn fertilizers that get into our waterways. And we can reduce pet waste, make sure that pet waste isn’t getting into our waterways and then we can look at reducing our carbon emissions,” Frignoca says.

She says sewage treatment operators are also taking steps to address the problem. Portland’s East End Wastewater Treatment Facility, for example, will need to reduce nitrogen 20-40 percent as part of a new permit requirement.

But in the meantime, she says Casco Bay is sending out a signal that conditions are changing and not for the better.