JOHANNESBURG — An acclaimed outdoorsman who wrote movingly about testing himself against nature is presumed dead after a crocodile snatched him from his kayak while he led an American expedition from the source of the White Nile into the heart of Congo.

Two Americans, including Chris Korbulic, of Rogue River, being guided by 35-year-old South African Hendrik Coetzee on the grueling trip, could only watch in horror. They paddled unharmed to safety after the Tuesday morning attack on the Lukuga River in Congo.

The International Rescue Committee, which runs development projects in the Central African nation, helped evacuate the Americans to a nearby town, Ciaran Donnelly, the organization’s regional director in Congo, said Thursday.

Coetzee’s body has not been recovered. The stretch of river where the trio was traveling is notoriously dangerous because of its whitewater, and the high density of crocodiles and hippos.

A friend, Celliers Kruger, who owns a South African kayaking company, called Coetzee a legend.

“He was the bravest guy I’ve ever known,” Kruger said. “But he wasn’t crazy. He was very calculated and set the bar high for future exploration in Africa.”

Paul and Mary Korbulic, of Rogue River, the parents of Chris Korbulic, said they were vacationing in Costa Rica when they got an e-mail from their son saying he was safe, but had no details of the attack.

“You just can’t even think how terrible that is,” Mary Korbulic said of the crocodile attack.

The two Americans — Ben Stookesberry and Korbulic — are currently in Congo but expect to return home to the U.S. shortly. Stookesberry is from Mount Shasta, Calif. Coetzee had been living in Uganda at the time of the expedition.

One of the Americans recounted on his blog how Coetzee has warned them about the dangers of the trip, including “three-ton hippos that will bite you in half.”

“Stay off the banks because the crocs are having a bake and might fancy you for lunch. Basically, stay close behind me and follow my lead. Any questions?” the blog quoted Coetzee as saying.