A team of stars including comic Dara O'Briain, actress Chelsee Healey and ex-Spice Girl Mel C is to brave crocodiles, hippos and huge rapids by tackling more than 100km (more than 60 miles) of the Zambezi River.
The group - which also includes Jack Dee, Radio 1's Greg James and triple jumper Phillips Idowu - will be pushed to the limit as they take on the back-breaking journey in dugout boats, canoes and white water rafts for Comic Relief.
They will be paddling for up to eight hours a day during the five-day ordeal as they negotiate the African river.
During the 111km (68-mile) journey, they will face rapids known as Gnashing Jaws of Death, The Washing Machine and Oblivion on their way to the world's largest waterfall, Victoria Falls.
Their BT Red Nose Challenge: Hell And High Water will see them shunning luxury accommodation en route and instead they will be camping on cliff-tops and watery riverbanks as they nurse their blisters and rest their aching limbs. Armed guards will accompany them to protect them from wild animals as they recharge.
Mel C, who is a veteran of Comic Relief projects after releasing a single for the charity with the Spice Girls in 1997, said: "It's going to be tough.
"It's going to be physically and emotionally demanding, but we've all got each other and hopefully we'll be able to get through it."
The journey, which it is hoped will raise £1 million, is being staged ahead of this year's Red Nose Day which takes place on March 15.
The proceeds will be used to help educate children in Zambia.
The stars can be sponsored at rednoseday.com/zambezi.