Kiwi conservationist Pete Bethune has walked out of a hospital in Costa Rica today after a deadly snakebite almost claimed his life two weeks ago.

He was bitten by the highly venomous Fer De Lance snake in a South American jungle just after Christmas.

Initially fearing he wouldn't make it out alive, Bethune managed a difficult three-hour trek, clambering and dragging himself through unforgiving terrain to reach his boat.

By the time he got to a hospital, his left leg had swollen to at least double the size of his right after the Fer De Lance viper sank its fangs into his lower calf.

But friend and spokeswoman for Bethune's Earthrace charity Larisa Kellett said Bethune has beaten the odds and walked out of hospital today.

Pete Bethune struggles down streams in the Costa Rican jungle after being biten by a poisonous snake. Photo / Supplied

She said it was a big relief for the team and Bethune was now back on his boat in Costa Rica.

Bethune, who is in Costa Rica to help stop wildlife poaching and illegal gold mining, described the first days of his stay in hospital as a blur.

"When I first came in here they put me on morphine. You are lucid in a sense of what's going on but it's very dream-like."

He said the doctor treating him told him he had been given the greatest level of antivenom of any snake-bite victim he had ever treated.

Bethune described the journey out of the jungle as one of the most extraordinary three hours in his life.