This is a timelapse of the annual tidal wave that races up the Qian Tang River in China twice-daily.
It reaches its peak around October/November. The effect is caused by the Earth rotating through the 2 tidal bulges of water (also of rock, to a lesser extent) that are attracted to our Moon as it orbits Earth once a month.
Once a year, a surfing competition is held at this very spot, where teams compete for which surfer performs the best tricks and style.
Towards the lower bank area, the muddy bottom is churned up, making the water appear darker all along the bank.
The water level can rise several meters, and even spill over the edge, which has been known to cause deaths in recent years.
