Each year spectators (thrillseekers?) gather and watch the tidal bore of the Qiantang River in east China. A tidal bore is the initial wave that is formed in an inlet or river by the leading edge of an incoming tide.
It's not as if they didn't know it was going to happen, as these images from past tidal bore viewing events show.
For hundreds of years, on the eighth month of the lunar calendar, people have gathered along the shores of China's Qiantang River at the head of Hangzhou Bay to witness the waves of its famous bore tide. Higher-than-normal high tides push into the harbor, funneling into the river, causing a broad wave that can reach up to 30 feet high. If the waves surge over the banks, spectators can be swept up, pushed along walkways or down embankments.
Come at me, tidal bore. Come at me.