A group of stand-up paddleboarders is passed by a landing craft used to transport trucks to and from the islands of Casco Bay off the coast of Portland in this July 11, 2019, file photo. A large algae bloom was spotted in Casco Bay that stretches from Chebeague Island to Phippsburg. Credit: Robert F. Bukaty | AP

State officials are monitoring a large algae bloom in Casco Bay that stretches from around Chebeague Island to Phippsburg.

Kohl Kanwit, director of the Maine Department of Marine Resources’ Bureau of Public Health, said Karenia mikimotoi is a nuisance species that turns the water rusty brown and can have a foul smell. But she said it has no effect on human health and safety, either by swimming or eating seafood caught in the water.

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Kanwit said if the bloom gets large enough, it can harm marine organisms.

“As the bloom declines, it can cause low oxygen levels and essentially suffocate marine organisms, but if the bloom isn’t large enough to cause that effect, then generally it’s fairly benign,” she said.

Kanwit said Karenia is typically found in warmer waters than off Maine. She said there was a similar large bloom of Karenia in 2017 that may have killed some soft-shell clams.

Kanwit said officials aren’t sure how Karenia showed up in Maine or why there’s been such a big bloom this year.

This article appears through a media partnership with Maine Public.