The skater makes it down to the bottom but as he starts to go up the next arch he loses momentum and control, and bails over the side of the concrete pillar.
The skateboard can be seen flying to one side, while the skater falls backwards and can be seen falling out of shot, head first, as traffic, including a truck, is queued up in the background.
Ward said he lived near the bridge and had seen the man riding his bike over the arches in the past.
"I was biking home and passed him with his skateboard, I said 'hello' to him and recognised he was the guy who I have seen biking over the humps on his BMX bike, although he nails that.
"So now he has nailed the BMX he has obviously decided to step it up and try it on a skateboard."
Ward said he was amazed to see the man get up and walk away after crashing.
"You wouldn't catch me up there. He is lucky he got up and walked away but you got to admire his ballsyness."
The video has now gone viral and shared nearly 1000 times on Facebook.
"Lots of people recognise the Fairfield Bridge and lots of people have heard myths, seen people occasionally walk or even bike but no one has seen anyone skate over it... so pretty stoked I caught it on my phone."
Waikato Road Policing Manager Inspector Marcus Lynam said it was "sheer luck" no one was killed or seriously injured.
"This is a reckless and dangerous stunt that put the skateboarder and other motorists at risk." The skateboarder had not been reported to police but anyone who witnessed "reckless behaviour like this" was encouraged to call 111 immediately, he said.
"Police take stunts like this extremely seriously and anyone endangering other road-users could face serious charges."
Auckland pro skater Simon Young, of Young Guns Skate School, described the bridge rider as a "madman" but said skaters were known to push their limits.
"It's pretty crazy. It's a good thing there's a footpath on the side.
"I think a lot of skateboarders, like that guy, would be looking for that adrenaline buzz, I guess. There's a lot of different styles of skateboarding, some people like to do big things like that. That would be the minority of skateboarders I think."
Young, who has been skating more than 20 years, said the man looked experienced.
"He wouldn't have tried that if he didn't think he was capable of doing it. It looked to me like he was capable of doing it and did get a bit unlucky. But I don't condone that sort of thing. It's not something I'd try, or a lot of skaters would try."
However, he doubted he would have made it up to the top of the other side because of losing speed in the valley between the arches.
"He would never have made it over the hump, he would have just gone up, about halfway. I don't think a skateboard would ever make it over there even if you're going full speed. I think a lot of your speed gets taken out by the quick drop in the middle."
He believed it was a stunt that no one had tried before - which is probably why the man tried it.
"There's a lot of good skaters and no one's ever dared to try that as far as I know, but I might be wrong."
The man's skateboarding is not the first stunt on the bridge to hit the headlines.
Mormon Few Stunt Crew rider Jonathon Bennett featured in a YouTube video in 2009, riding his 250cc trial bike over the 70cm-wide arches.
Although Bennett's ride was successful, he was prosecuted by police.
