09/24/2026
We're closely tracking a harmful algal bloom currently affecting Casco Bay, known as a Karenia bloom. It's having a real impact on aquaculture farms and wild harvesters, and it's a serious event for our working waterfront and ocean farming industries.
Researchers and community volunteers are watching closely as the bloom expands further north into Penobscot Bay, and we will be keeping a close eye on this and how we can help the affected industries navigate this challenge.
Our Aquaculture Program Manager Carissa Maurin explains that this bloom causes deoxygenation, which is most severe at the seafloor as the decomposing algae sinks, with the lowest oxygen levels typically occurring overnight and into early morning. This stresses shellfish, lobsters, and marine worms, and in some cases leads to mortality.
With a strong nor'easter approaching, we know many farms are sinking gear now for storm protection, and that should remain the priority. Carissa suggests that when the nor'easter passes and conditions are safe, farms should float or raise their gear again as soon as possible to minimize deoxygenation stress on the animals. Another risk management tactic is to reduce the density of your stocks and increase aeration in upwellers. Wild harvesters should also avoid harvesting during the bloom to reduce added stress on organisms.
An important thing for people to know — this particular bloom is non-toxic and not harmful to humans. People should feel confident continuing to buy and eat local seafood.
Learn more about the bloom and how to spot it here:
Below are updates DMR has issued to Maine's shellfish industry and interested parties regarding the recent bloom of the phytoplankton Karenia Mikimotoi. Announcements are arranged chronologically with the most recent listed first.