A tidal bore is a rare natural phenomenon in which an incoming tide creates a wave of water that travels up along a river or a narrow bay causing water to flow against the river’s current.

Tidal bores occur in relatively few locations worldwide. In fact, for bores to occur, there are a few conditions that has to be met: the river must be shallow, must have a narrow outlet to the sea and a broad funnel-shaped bay. The bay must also have large tidal range - typically more than 6 meters between high and low water. The funnel-like shape not only increases the tidal range, but it can also decrease the duration of the flood tide, down to a point where the flood appears as a sudden increase in the water level.

Tourists gather on the bank of the Qiantang River to see the soaring tide in Haining, Zhejiang province, on September 13, 2011. Photo credit