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Through statistical analysis of the red tides that occurred in the coastal waters of Tianjin from 2001—2020, it was found that in recent years, the occurrence of red tide in Tianjin coastal seawater exhibits high-frequency, small-scale characteristics. The annual cumulative duration of red tide from 2012 to 2020 shows a general increasing trend, which is mainly controlled by DIP. Summer months were the peak periods of red tide, especially in June and August, the duration of a single red tide was long. Red tide causing species was evolving toward dinoflagellates in the Tianjin coastal seawater. Noctiluca scintillans, Skeletonema costatum and Pseudo-nitzschia pungens caused the most red tide, these three types of algae have the characteristic of alternating over time to become the causing species, mainly due to their adaptability to the hydrological environment. Toxic red tides mainly occurred from June to September, the red tides that occurred in September were mostly toxic. The toxic red tide species in Tianjin coastal waters are mostly Cochlodinium polykrikoides and Gymnodinium mikimotoi.