Pfiesteria is a dinoflagellate microorganism that lives in estuarine areas. It has a complex life cycle with 24 different forms, several of which can release a toxin with both human and environmental effects and implications. Some Maryland watermen and State employees became sick after exposure to Pfiesteria -infested waters. It is important to understand that the illness is not caused by consumption of fish or shellfish. Both remain safe to eat.
Illness is caused by exposure to toxin in the water, either through contact or inhalation.
The toxins also affect fish, causing lesions and death. Once areas are known to have toxic Pfiesteria , local health departments, with State support, can close those waters to keep people away from potentially hazardous areas. Research indicates that toxic Pfiesteria blooms occur in nutrient enriched areas, with poor flushing and low flows. The actual trigger for production of the toxic forms of Pfiesteria seems to be the presence of fish, particularly oily fish like menhaden. Scientists don't yet understand the connection between nutrients and Pfiesteria .