Deadly Waters (E09)

Kayaking legends Ben Stookesberry and Chris Korbuic accumulate together hundreds of first descents in the most dangerous rapids in the world. But one river has left a mark on them. The calm waters of the Lukuga River, in Congo, hide one of the biggest concentrations of crocodiles on Earth. In 2010, they paddled through it with their mentor Hendri Coetzee. That was the last time they saw him. (National Geographic)