Qiantang River runs from the west to Hangzhou Bay in the east. It serves as a river hinge, playing an important role in the water-transportation between the east and the west. The extraordinary surging tide of the Qiantang River is a world-renowned natural wonder caused by the gravitational pull of the stars and planets. The centrifugal force produced by the rotation of the earth and by the peculiar bottleneck shape of Hangzhou Bay makes it easy for the tide to come in, but difficult for it to ebb.The soaring tide of the Qiantang River is such a marvelous spectacle that only the Amazon River's surging tide rivals it! Annually, millions of people from both home and abroad flock there to watch the magnificent tide on the eighteenth day of the eighth lunar month (also around the Mid-Autumn Day). When the surging tide comes, the water can rise up to a height of 30 feet and the noise it generates sounds like thunder, or thousands of horses running. Various activities will also be held to celebrate the annual Tide - Watching Festival, according to local custom.