A red tide measuring 780 square km in size has been detected in waters near east China's city of Rizhao, according to a notice issued Saturday by the State Oceanic Administration (SOA).

The SOA's North Sea branch, located in the city of Qingdao in Shandong province, said algae samples taken from the waters by a marine patrol vessel have tested negative for toxins.

The red tide is the first to be detected in the East China and Yellow seas this year.

The SOA notice said that the red tide was caused by a bloom of Noctiluca scintillan, a species of algae.

SOA said it will use satellite remote-sensing technology, patrol vessels and helicopters to monitor any changes in the red tide.

Although nontoxic, the algae may stick to the gills of fish and cause them to suffocate. The density of the algae increases with rises in water temperature and salinity, and the outbreak may cause damage to the fishery and aquaculture industries, the SOA said.