Rondon expected the River of Doubt to pour into the Madeira River, which was a principal tributary of the Amazon. He sent a detachment of men there to await the expedition’s arrival. The Madeira Basin is twice the size of France and the river winds for 2,000 miles through western Brazil. If Rondon’s predictions were correct, Roosevelt would have placed on the map a river of almost 1,000 miles and the group would have survived a journey “as perilous as any in the history of Amazon exploration” (130). Aware that the River of Doubt would have rapids, the group decided to harness its strength and head downstream. This strategy meant that there was no turning around. The group would follow the River of Doubt to its end or die.

Given the loss of the pack animals, the group arrived at the River of Doubt with no boats. Rondon arranged for the purchase of seven “roughly hewn dugouts” (134), which were hollowed-out tree trunks, from the Nhambiquara people. These boats were heavy and would be difficult to maneuver in the water. In addition to the challenge of navigating the river, the group faced potential encounters with several deadly predators, including South American alligators, anacondas, piranhas, insects carrying diseases, serpents, and poisonous frogs.