The National Oceanic & Atmospheric Administration agency said Thursday that two species of the microbes, called Pfiesteria, can transform into toxic organisms that cause fish kills. The microbe, which starts out harmless, shut down some North Carolina and Maryland waters in the mid-1990s. JoAnn Burkholder, a scientist at North Carolina State University, helped discover the organism in state waters in 1989. But her work was questioned by others who doubted that Pfiesteria spewed poison to attack estuarine fish.

After nine years of study, the oceanic and atmospheric administration and chemist Peter Moeller identified the venom - a discovery Burkholder praised. "The past nine or 10 years have been difficult. I really would not have wanted to live them. But this is a great day," Burkholder said Thursday.

Environmentalists have praised Burkholder's work despite the doubts raised by other scientists and public health officials. - AP