Pfiesteria complex organisms (PCOs) were claimed to be responsible for large fish kills in the 1980s and 1990s on the coast of North Carolina and in tributaries of the Chesapeake Bay.

[2] Pfiesteria was discovered in 1988 by North Carolina State University researchers JoAnn Burkholder and Ed Noga.

Early research resulted in the hypothesis that Pfiesteria is a predatory dinoflagellate that acts as an ambush predator, utilizing a "hit and run" feeding strategy.

Release of a toxin paralyzes the respiratory systems of susceptible fish, such as menhaden, causing death by suffocation.

[6] Pfiesteria biology and the role of PCOs in killing fish and sickening humans have been subject to several controversies and conflicting research results over the last few years.