[4] The river then runs through the Campos Amazônicos National Park, a 961,318 hectares (2,375,470 acres) protected area created in 2006 that holds an unusual enclave of cerrado vegetation in the Amazon rainforest.

The Roosevelt-Rondon expedition was the first non-Amazonian-native party to travel and record what Rondon had named the "Rio da Dúvida", then one of the most unexplored and intimidating tributaries of the Amazon.

They covered nearly 1000 miles in a 33 day period, following waters that eventually fed into the Aripuanã River[7] Roosevelt later wrote Through the Brazilian Wilderness recounting the adventure.

[9][10][11] This expedition consisted of a total of twenty persons including professional river guides Joe Willie Jones, Kelley Kalafatich, Jim Slade, and Mike Boyle, photographers Carr Clifton and Mark Greenberg, cinematographer Joe Kaminsky, Haskell's son Charles 'Chip' Haskell Jr. who served as the expedition's communications expert, Brazilian scientists Geraldo Mendes dos Santos and João Ferraz (ichthyologist and pharmacologist), and chiefs Oita Mina and Tatataré of the Cinta Larga tribe whose land borders much of the river.

[12] A documentary of the expedition was subsequently produced and aired on PBS called the New Explorers: The River of Doubt narrated by Bill Kurtis and Wilford Brimley.

[13] Since this time, the expedition has inspired others to undergo its challenges such as Materials Science Professor Marc A. Meyers, Col. Huram Reis, Col. Ivan Angonese, and Jeffery Lehmann.