The pororoca is a tidal bore, with waves up to 4 meters high that travel as much as 13 kilometers inland upstream on the Amazon River. Its name comes from the indigenous Tupi language, where it translates into “great destructive noise”. It occurs at the mouth of the river where river water meets the Atlantic Ocean. The phenomenon is best seen in February and March.
It is best seen when there are changes in the phases of the moon, basically two days before until three days after. It happens particularly on the equinoxes of each hemisphere and it reaches its highest intensity when the moon is either full or new.
The phenomenon, upon elevating the leval of the oceanic waters, makes them invade mouths of the rivers, abling the formation of waves up to ten meters thick and three to five meters high with a speed of 10 to 15 mph.
The wave has become popular with surfers. Since 1999, an annual championship has been held in São Domingos do Capim. However, surfing the Pororoca is especially dangerous, as the water contains a significant amount of debris from the shores of the river (often entire trees). In 2003 the Brazilian Picuruta Salazar won the event with a record ride of 12.5 kilometers during 37 minutes.
Along the branches or “caños” in the Orinoco Delta, pororoca is known as macareo, which is also the name of one of these branches.
Here’s the trailer
And here’s a description of how it happens