Arriving in the remote town of Tapirapoan, it took the travelers two months to reach the river. They arrived in February 1914, with insufficient supplies and a depleted team. On the deadly river itself, they were beset by huge, vicious flies, swarms of mosquitos, the danger of alligators, and rapids they had sorely underestimated. Soon after beginning the journey, History reports, Teddy Roosevelt was bitten by a deadly coral snake, perhaps surviving only because its teeth didn’t penetrate his boot.

Kermit narrowly survived after his canoe capsized (one companion drowned in the incident), while a dispute over food saw one member of the party shoot another to death (the killer fled into the jungle). Roosevelt himself developed fever and delirium from a badly infected leg (which had been slashed by a jagged rock), having to undergo desperate impromptu medical care by the side of the river. At his lowest ebb, he reportedly begged his companions to leave him to die to help their own chances of survival.

On April 26, along with son Kermit and 18 other survivors, he reached some friendly locals, the area where the River of Doubt met the Aripuanã River, and the end of the voyage. The next month, Roosevelt was back in New York and on the mend. The validity of the group’s scientific findings was backed up by further expeditions, and the River of Doubt came to be known as the Roosevelt River. It still is.