Annual Liffey Swim: Ian O'Riordanmeets the remarkable Joe Oakes, who gives a new meaning to the term Ironman.

Joe Oakes emerges from the Forty Foot, shakes down his impressive physique - the gymnasium shoulders, the Charles Atlas chest - and slowly removes his swim cap.

"Just had an idea," he says. "I'm going to start the Howth duathlon. Swim from here to Howth. And then take the Dart back into Dublin."

The 20-minute swim in Dublin Bay must have heightened his humour, because he was obviously joking about that. There's no way Joe Oakes would take the Dart back from Howth. He would either run, bike or simply swim back.

With that, he asks some local swimmers about the exact distance. They look at him with mild bemusement, this 73-year-old with a soft American accent, wondering if he's serious. If they realised they were talking to Alcatraz Joe, they'd know he was deadly serious.

He then notices a jellyfish sting on his arm, and displays this with honour.

As he dries himself off with a small hand-towel he talks about some of his previous excursions across open water, including the English Channel, the Strait of Gibraltar, the Dardanelles (from Europe to Asia) and the freezing Bering Strait, from Russia to Alaska.

The small tattoo on his right arm with the word "Nessie" is a souvenir of the "pretty cold" swim across Lough Ness.

It must have been cold, because Alcatraz Joe has only once worn a wetsuit, and he clearly reflects on that as a mistake.

Of course, his favourite swim, and the one he'll always be associated with, is from the old penitentiary island of Alcatraz back to Pier 39 in San Francisco harbour. For years this was understood as "unswimmable", but Oakes has helped change all that, thus earning the classic nickname.

For almost 30 years now he's been guiding swimmers, maybe 25,000 or more, across that cold and turbulent stretch of water, and his book The Alcatraz Swimmer's Manual is now in its fourth edition.

In all those years only one swimmer didn't make it. That was back on August 8th.

"But you know, I was a runner first of all?" he adds, as if to change the subject.

"I started running in high school, in the Bronx, back in 1948. When I realised no one would pay me for running, I got a job as a lifeguard, and that's where the swimming started. Later, in 1979, I heard about this Ironman triathlon down in Hawaii, which was just starting up. I've done that half a dozen times, and after that I got more interested in the swimming aspect."

That's why he's in town, to participate in tomorrow's annual Liffey Swim. Heuston Station to the Custom House will feel like a short crawl for this positively unique and inexpressibly impressive man.

Naturally, Alcatraz Joe still runs and bikes when he can, but reckons where he lives now, in Portland, Oregon, is too dangerous for cyclists.

"American roads just aren't compatible with cyclists," he says.

Not that he's given up on those sports.

In 1981, after completing his first Ironman, he founded the "Escape from Alcatraz Triathlon", shorter than Hawaii, but just as punishing - not just because of 15-mile cycle over Golden Gate Bridge and 14-mile run over the brutally hilly Dipsea Run in Marin County.

"We had to include a 10-minute run after the swim," he explains, "because when they come out of the water they're just too cold to get straight on the bike."

Even in his later years, Alcatraz Joe has been looking for more extreme ways to test his body.

Like the time of his "Triathlon across America", which meant swimming across every river he met, in between a daily run and cycle.

In fact, he's effectively done the first "world" triathlon - his non-motorised circumnavigation of the earth, which also included sailing, kayaking and dog-sledding. That took 10 years to complete, in various stages.

"The hardest one?" he repeats, when asked the question. "That would have to be the Death Valley ultra-marathon: 135 miles. You start at the hottest and lowest point in the country, and run to the highest point, Mount Whitney. You have to wrap duck-tape around your feet to prevent the skin from burning off."

What doesn't kill you makes you stronger.

Seems like those words were written by you, Alcatraz Joe.