Check out this point-of-view video of kayaking the Congo shot by Andrew Maser of Rivers in Demand, courtesy of The Adventure Blog. Outside's Kyle Dickman is in some of the shots! If it weren't for the distant shoreline, you'd think they were on the ocean. The Congo is the eighth longest river in the world, stretching 2914 miles. It also has the second highest volume of any river, surpassed only by the Amazon, and sometimes reaches depths up to 750 feet.
You can read a good article about their trip here, at Smithsonian.