On August 14th Heterosigma akashiwo, a raphidophyte plankton, was identified in water samples collected from the Middle River, Chesapeake Bay; counts are low but the species is present in virtually every tributary in the Middle River system. The highest count was 318/ml from Hopkins Creek. In Maryland, H. akashiwo was first identified in the Chesapeake Bay during 2002 in the Middle River.

An unidentified ichtyotoxin (i.e., fish-killing toxin) has been speculated as the causative agent in the net pen fish kills elsewhere in the world related to blooms of H. akashiwo. There are no documented effects to humans from such blooms. No fish or human health effects have been associated with this species in Maryland waters.