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Environment and Outdoors

Scientists Say Casco Bay’s Algae Bloom Is Retreating

Fred Bever
Maine Public
Department of Marine Resources biologist Bryant Lewis takes samples in South Portland.

State marine officials say an unusual algae bloom in Casco Bay may be retreating, but they say it still poses a toxic threat to fish.

Department of Marine Resources biologist Bryant Lewis sampled water up and down the coast, including at a South Portland dock. He’s measuring oxygen levels and the prevalence of an invasive Asian algae — Karenia mikimotoi — that has turned parts of the bay an unusual brown and unleashed an unpleasant, rotting fruit smell.

He says levels have dropped since last week.

“Yeah this water looks nothing like a week ago. I mean it was such dark brown it was almost black. It’s a good sign that the water’s looking like this,” he says.

But he adds that as the plankton dies off and falls down the water column, it will be consumed by bacteria, taking up oxygen and potentially suffocating fish and bivalves. DMR officials say the potential for die-offs may now be at its highest.

Fishermen and harvesters in Casco Bay should stay alert, officials say, with the highest risk at night and in the early morning. They add that the algae does not pose a threat to human health.