SOUTH PORTLAND — A growing spread of green algae that has returned for the second consecutive year could threaten the health of Casco Bay.
The blooms were first noticed on June 21, several weeks earlier than last year. Environmentalists said they don’t know what’s causing the fibrous mats of algae, which have been spotted in several places.
Friends of Casco Bay is monitoring the blooms in South Portland’s Mill Cove and Pleasantdale Cove, Portland’s Back Cove, and Basin Cove in Harpswell.
The algae can suffocate species that are important to the health of the bay, including clams, worms and other small organisms. It also makes it difficult for birds to eat, because the algae is difficult to penetrate, said Mike Doan, a research associate with the group, a nonprofit founded in 1989 to improve and protect the environmental health of the bay.
He said the organization has received reports of other blooms in the bay and will be inspecting them, too.
The algae bloom was seen last year for the first time in several years. The fact it’s come back this year is worrying those who track the health of Casco Bay.
“It is alarming — this is a problem,” said Ivy Frignoca, Casco Bay keeper. “We are trying to figure out what is happening in the bay that is conducive to these blooms. They create problems in clam flats.”
Doan said the algae bloom this year was is also more widespread than it was a year ago.
He said what is especially troubling is that the algae returned for a second year in a row under markedly different weather conditions. Last year, it was dry and sunny, while this year has been more rainy and cloudy. This has enabled researchers to rule out weather conditions as a cause.
The organization is conducting DNA tests to determine what kind of algae is causing the problem.
Doan said he suspects nitrogen pollution could be the culprit, but more research needs to be done.
He said some nitrogen is essential to plants and animals, but “nitrogen pollution is one of the biggest concerns,” especially in amounts “over and beyond what should be there naturally.”
If nitrogen pollution is the problem, limiting stormwater runoff, lawn fertilizers, pet waste, and other nitrogen-carrying elements from the bay could help, Doan said. Making sure septic systems are working properly will also help prevent runoff.
Cutting back on the use of fossil fuels will also prevent nitrogen from entering the atmosphere, and eventually, the water.
Residents can report large algae blooms by emailing slimewatchers@cascobay.org. Photos and locations with coordinates and landmarks are helpful, Doan said.
Algae coats Mill Cove in South Portland during low tide on July 14. Friends of Casco Bay is monitoring the growth and three others in South Portland, Portland and Harpswell. Other blooms have been reported and the organization will be visiting the areas to investigate.
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