After regular beatings from his father, Martin Strel would take refuge in a barn on his family’s chicken farm in Slovenia. Snuggled up amongst the chooks, the cheeky boy would dream of a time free from torture. “My father was a hunter,” says Strel. “I think [the beatings made me] much stronger. My body is like iron.”

Strel went on to become a world record holding endurance swimmer and believes his ability to endure extreme pain helped him achieve his remarkable feats. He holds the records for continuous swimming (504km over 84 hours in 2001) and the longest swim: 66 days paddling the entire length of the world’s most hostile river, The Amazon, in 2007. “I was always looking where I can go beyond the limits,” says Strel, 55, while in Australia during June’s Sydney Film Festival to promote the documentary of his Amazon trip, Big River Man, which is in cinemas now and on DVD from November 27. “Everywhere I was told, ‘Don’t do this. You will die.’ Now this film sometimes make me cry. It’s done. I’m still alive.”

Strel’s emotion is more than justified: he miraculously dodged all types of predators. “I don’t worry about me,” says Strel, who was dubbed The Fish Man in South America. “But it was very close [to death]. You never know what is below the water. The Amazon is not so friendly. You have many piranhas, anacondas, snakes, pirates, sharks, rapids. And the water is muddy so it’s not possible to see anything. Everything is against you.”

He wasn’t so lucky, however, when it came to piranhas, parasites and the scorching sun. He received second-degree burns and resorted to fashioning a swimming mask that made him resemble the Creature From the Black Lagoon. “I got a lot of parasites, schistosomiasis it’s called, but I’m healthy now,” says Strel, showing off a six by two inch chunk a 50cm piranha took out of his back. “If piranhas touch your body it’s like a fire. They have very sharp teeth. Piranhas touched me many times but I wasn’t attacked by thousands. If you put blood somewhere else you divert them.” So his crew scattered pig and chicken blood to distract them.

Starting in Peru weighing 115kg, when he finished in Brazil 5,400km later, 175cm Strel weighed 99kg and was taken to hospital because his blood pressure was so high he was at risk of a heart attack. But the physical challenges weren’t as huge as the psychological ones. “Mental preparation is the most important,” says Strel who would rise before sunrise to swim for six hours, take half an hour’s lunch break then return to the murky water for another five or six hours. “I‘m alone. There’s no competition. There’s fighting between nature. It’s not possible to be stronger than nature—and the sun too—but you must be close to it.”

Strel, whose previous swims include the 3,004km-Danube in 2000, the 3,797km Mississippi in 2002 and the 4,003 km Yangtze in 2004, has developed an ingenious way to keep going. “Swimming is not like running where you can talk and see things,” he says. “Below the knee it wasn’t possible to see anything. I talk to myself, make up stories, films, everything, in order to forget about swimming and the pains. I’m like a robot. I know how to hypnotise myself and after I wake myself I’m a different man, reborn, fresh, but, most important, with no pain.”

Also extraordinary is Strel’s refusal to restrict himself like other sportsmen: he may be disciplined about training but he is overweight, old by elite athlete standards and a self-confessed lush who downed numerous beers and up to two bottles of Slovenian wine every day of his swim, even drinking it while in the water. “It is called Cvicek,” says Strel, who believes the wine, which he says has less sugar and alcohol than most, is good for his health. “This is not like wine here in Australia. This is very special wine, less that 9%, and it makes your body stronger.”

His son and manager, Borut, 28, who recently completed his computer science degree, no longer worries about his father’s outlandish challenges. “He is a bit crazy, you have to be to do these things,” says Borut, who laughs heartily with his dad when he adds: “You can’t be normal.”

“I’m more worried when he does other things like being too drunk when driving,” says Borut who describes his father as “a special man, unique, sometimes strange, misunderstood, and with lots of endurance, determination, stamina.”

Strel’s student daughter, Nina, 24, and architect wife, Nusa, 48, stayed safely at home in Slovenia. “I am a different man in the boat,” says Strel. “[My wife’s] life is totally different. It’s better to be away from me and then I come home.”

Apart from his personal desire to attempt incredible feats, the former professional gambler and flamenco guitar teacher had a serious reason for getting wet: to promote environmental issues including pollution and deforestation. He swims, he says, “for peace, friendship and clean water.” Who could argue with that?

* Big River Man has been released in most capital cities and opened in Adelaide, Brisbane and Melbourne on October 29.

* It features at the Gold Coast Film Festival on November 12 and is available on DVD on November 27.

* More info: amazonswim.com