The pororoca (Portuguese pronunciation: [poɾoˈɾɔkɐ]) is a tidal bore, with waves up to 6 metres high that travel as much as 13 km inland upstream on the Amazon River and adjacent rivers. Its name comes from the indigenous Tupi language, where it translates into "great destructive roar". It occurs at the mouth of the river where river water meets the Atlantic Ocean. As the fresh water from the river is less dense than the ocean water, it overlaps the rising tide therefore delaying it. At some point the balance is disrupted, and together with the winds the wave grows and spreads over inland, thus inverting the river current. The phenomenon is best seen in February and March.
The wave has become popular with surfers. Since 1999, an annual championship has been held in São Domingos do Capim (on the adjacent Guamá River). 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 addition to dangerous fauna.
Wave height: 3 to 6 meters
Wave run: 40 minutes How often: every 12 hours
Distance covered: 30 km in over one and a half hour Speed: approx. 20 km/h