Algal Bloom Intensified off Maine Coast

Phytoplankton patches have expanded along the Midcoast following recent heavy rainfall.

Updated on Oct. 6, 2026 in Current Conditions

A wide, elevated view of Maine's rocky coastline showing discolored olive-green patches floating on the deep navy surface of the Atlantic Ocean. — Phytoplankton blooms have intensified along Maine's Midcoast following recent heavy rainfall, according to state environmental officials monitoring the marine environment. AI Illustration. Upload story photo >

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An algal bloom of the phytoplankton variety Karenia mikimoitoi has intensified off the Maine coast in recent weeks. While patches remain active from the Midcoast to Penobscot Bay, the bloom has begun to dissipate in inner Casco Bay.

Why it matters

Climate change is increasing the frequency, size, and duration of such blooms by fostering warmer marine environments. These events pose environmental risks by reducing oxygen levels in the water, which can affect marine life.

Satellite footage identifies bloom patches ranging from one half mile to five miles offshore. Recent rainfall triggered the offshore intensification of the Karenia mikimoitoi phytoplankton.

The details

The algal bloom affects local marine health by lowering oxygen content in the water, a process that can harm fish through their gills. Officials have confirmed that Karenia mikimoitoi is not toxic to humans, and Maine seafood remains safe to consume.

The algal bloom spread off the Maine coast over the past weeks.

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Sept. 28
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Seasonal Patterns

The link between climate-induced warming and bloom intensity follows patterns documented by the National Oceanic and Atmospheric Administration's tracking of harmful algal bloom frequency. This event follows a documented pattern where rising marine temperatures extend the duration and geographic reach of phytoplankton blooms.

Residents should continue to report instances of discolored water to the department via email to assist with ongoing mapping. There is no threat to human health from the bloom, and local seafood remains safe for consumption.

The takeaway

While the bloom creates an unpleasant environment for marine life, it does not pose a direct toxic risk to the public. Residents can expect to notice stronger odors as the bloom eventually collapses and decomposes.