Red tides have been detected in Ningbo and Wenzhou along the coast of Zhejiang. Red tides are a type of marine hazard that is formed by excessive algae density.
When red tides are formed, the sea appears pink or even brick red during the day, and blue at night. "Blue tears" are the phenomenon of marine luminescence caused by plankton stimulated by the outside world, which generally occurs from March to October every year, especially in late spring and early summer. The sight of "blue tears" at night is a non-toxic red tide.