From Delaware to North Carolina, a formerly unknown species of toxic algae has been implicated in an alarming series of fish kills and associated human illnesses. This program scrutinizes the dinoflagellate known as Pfiesteria piscicida. Discovered by researchers at North Carolina State University, P. piscicida is now known to have a highly complex life-cycle with dozens of reported forms, a few of which can produce potent toxins. What has triggered this organism—a common indigenous inhabitant of mid-Atlantic coastal waters—to suddenly become a sensational health hazard and the focus of widespread panic? (28 minutes)