First of all, the tide is the highest around the 15th of every month. Secondly, in August, the southeast wind prevailed in that area, and the wind blew a lot of seawater into the estuary, while the Qiantang River estuary was trumpet-shaped, which easily caused the seawater to flood in and rise. At the same time, there is abundant precipitation and a lot of rivers. All these led to the biggest tide in Qiantang River on August 15.