A red tide could hit the waters north of Pingtan, as the province enters an active red tide season, said marine authorities on May 6.

The Fujian Provincial Department of Ocean and Fisheries sent the warning after a red tide bloom spread over 75 square kilometers on May 4 off waters near Sansha Bay in Ningde city, north of Pingtan county.

Red tide is a common name for a phenomenon known as an algal bloom (large concentrations of aquatic microorganisms) caused by a few species of dinoflagellates that take on a red or brown color.

It is usually found in coastal areas and is sometimes toxic to fish life and, through accumulation in shellfish, to humans.

Red tide resulted in a direct economic loss of roughly 2 billion yuan ($3.26 million) last year. Ten red tide blooms were recorded from May 18 to June 8 in 2012, affecting waters of over 323 square kilometers and resulting in the death of shellfish and abalone during the span.

Edited by Chen Zhilin and Michael Thai