The pororoca — “great destructive noise” in the indigenous Tupi language of the Amazon Basin — is a tidal bore that occurs in February and March at the mouth of a river in the Amazon where river water meets the ocean. The leading edge of the incoming tide forms waves of water that travel 20 miles, and farther, upstream against the direction of the current, with waves up to 12 feet high.
Surfing the Pororoca is especially dangerous because the water contains a significant amount of debris from the shores of the river — including entire trees — as well as some nasty critters.
Serginho Laus, a professional surfer, broke the world record for surfing the Pororoca in the Araguari River for the second time on June 8, 2009 when he rode one wave for a distance of almost 21 miles.
The Pororoca on the Araguari River is considered one of the most dangerous.
But you don’t want to get to close to the one on the Qiantang River in China — the world’s largest: