Maine DMR: Maquoit and Middle Bay stay closed as the Karenia bloom shifts

Two Casco Bay shellfish flats are still closed because of the Karenia mikimotoi bloom. The Maine Department of Marine Resources’ Sept. 23, 2026 update to the industry restates an emergency rule, effective Sept. 19, that shuts the entire intertidal growing area of Maquoit Bay in Brunswick and the eastern side of Middle Bay in Harpswell. The commissioner adopted it under 12 M.R.S. §6171(3)(A) so harvesting would not add stress and mortality while the bloom is on those flats. It is a resource closure, not a “do not eat” order.

DMR says this phytoplankton is not toxic to people. Shellfish and fish taken from Maine waters are still safe to eat, and growers, harvesters, and dealers may keep selling product that meets the usual sanitation rules. Outside those two closed areas, the bloom is not a public-health shutdown.

The Sept. 23 note, drawing on NOAA satellite imagery that does not identify the species by itself, describes an active bloom from northern Massachusetts to the Jonesport area and offshore across much of the Gulf of Maine. It looks densest offshore from Phippsburg to Vinalhaven, with very dense pockets in western Penobscot Bay. Coastal sampling is what DMR is using to treat Karenia mikimotoi as the dominant species, and the satellites only see the surface. Inner Casco Bay has eased — lower cell counts and less discoloration — but a collapsing bloom can pull oxygen down, and DMR expects more dead shellfish and marine worms there. Western Penobscot Bay, between Owls Head, Northport, and Islesboro, plus a dense patch south of Vinalhaven, is intensifying. Harvesters have reported discolored water in Stonington.

Watch for water that runs rust, brown, or nearly black, and a smell that gets worse as the bloom breaks down. Softshell clams and marine worms are the animals most likely to die. Fish, and lobsters that are free to move, are less so; a lobster in a trap or crate is not. DMR says any toxins this species makes are thought to act on gills at contact and not move up the food chain. Report discolored water or dead marine life to DMRPublicHealthDiv@maine.gov, and check the live closure map before you dig.

This is a The Gillnet news desk summary, not a reprint.

Source: Maine DMR — Updates on the Karenia mikimotoi bloom (Sept. 23, 2026).