Maine Officials Tracked Phytoplankton Bloom

The Maine Department of Marine Resources identified the bloom in Casco Bay, though it poses no threat to humans.

Updated on Sept. 18, 2026 in Aquariums

Gouache-painted illustration of a lone ocean research buoy in dark, hazy Atlantic waters near a distant Maine coastline. — The Maine Department of Marine Resources is monitoring a phytoplankton bloom in Casco Bay that has caused local shellfish mortality but poses no human health risk. AI Illustration. Upload story photo >

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Is your local area sufficiently prepared for the environmental impacts of recurring coastal phytoplankton blooms?

State officials identified a Karenia mikimotoi phytoplankton bloom stretching from the Maine-New Hampshire border to Penobscot Bay. While the bloom has caused local shellfish and fish mortality, authorities confirmed it presents no danger to human health.

Why it matters

The bloom impact mirrors events from 2017 when similar conditions led to significant clam and lobster losses in the region. State guidance aims to help municipal officials and shellfish growers navigate potential ecological disruption during the bloom.

Official water sampling confirmed the presence of Karenia mikimotoi on September 8 in Portland Harbor. Cell counts in Casco Bay are now showing a downward trend following an initial surge.

The players

Maine Department of Marine Resources

This state agency manages and protects Maine marine resources and is responsible for monitoring the coast.

Maine Marine Patrol

This law enforcement branch of the Department of Marine Resources patrols state coastal waters to ensure public safety.

The details

Marine Patrol first signaled the event by capturing flyover images on September 7, prompting intensive water sampling. Although the organism is harmful to aquatic life, state health experts have cleared it as safe for human contact and consumption.

A similar bloom in 2017 lasted for 3 weeks.
Marine Patrol captured images of the bloom on September 7, 2026.
Water sampling confirmed the presence of the phytoplankton on September 8, 2026.
Cell counts in Casco Bay showed a downward trend between September 14 and September 18, 2026.

Culture Shift

The current bloom follows a clear historical precedent set by the 2017 Karenia mikimotoi outbreak. Scientists use these recurring events to refine models of coastal ecosystem resilience in the Gulf of Maine.

Residents and tourists are advised that the bloom poses no risk to human health despite visible discoloration in coastal waters. Shellfish growers should continue following guidance issued by the state as officials monitor the situation.

The takeaway

While the bloom is currently trending downward, those in the region should follow state updates regarding water safety. Consistent monitoring by state agencies remains the best tool for protecting local shellfish harvests.