The extraordinary surging tide of the Qiantang River is a world-renowned natural wonder caused by the gravitation of the celestial body and the centrifugal force produced by the earth's rotation. Meanwhile, the peculiar bottleneck shape of the Hangzhou Bay also contributes to the spectacle.

The Qiantang River is 410 kilometers long -- the longest river in Zhejiang Province. To the east of Zheshan Hill on the southern banks of the river is a vast area of reclaimed land (like a peninsula) to keep off the river mouth and to make the area from the hill to the outside 12th section like a large-sized bottle with a small mouth. The tide can come in easily, but ebbs with difficulty. The Hangzhou Bay is over 100 kilometers wide and narrows only about several kilometers up to the outside 12th section. However, since the eastern part of the riverbed is also sharply raised, when a great quantity of water from the Qiantang River mouth arrives, the tide cannot be raised evenly due to narrowed-down river area. Then, the rear tides pushes front tides since the front tides are not fast enough; one wave upon another, they form tides more than eight meters high, with the speed of more than 10 meters per second. The roaring tides thunder with a sound like that of thousands of charging troops.

The tide was formed as early as in the Eastern Han Dynasty (25-220) and people have been watching the Qiantang Tide since the Tang dynasty (618-907). During the Southern Song Dynasty (1127-1279), the tradition was observed in an unparalleled way. The 18th day of the eighth lunar calendar is said to be the best time to enjoy the spectacle. Over time, the tradition of tide watching has become a grand occasion and local people organize various festivals to celebrate it. When a tide-watching festival arrives, people from all over the country and the world come to watch the natural wonder.