Surfing the Amazon

The pororoca is a tidal phenomenon that occurs at the mouth of the Amazon. Every year around February or March, the high tide coming in from the Atlantic Ocean forms a wave that travels up the Amazon, against the river current.

It's effectively the longest ridable wave in the world with some rides lasting over 30 minutes. The Amazon poses hazards for surfers, namely crocodiles, river sharks, and (even scarier) candirús, which are parasitic fish that swim up the penis.