About 10.30am, Stephen Donnelly, Chris Willans, Michael Davies and John Keys were standing on the edge of the Coomera Houseboats Holidays car park 'admiring the view' when the concrete edge and railing fell into the water, taking them with it.
"It all happened in half a second -- there were four of us admiring the view and all of a sudden the whole thing collapsed, the fence and the concrete slab," said Mr Donnelly.
"One of the guys was pinned underneath the water for about 15 seconds by part of the fence and we just kicked at the fence and fortunately some rocks moved and he was able to get out.
"I thought I was all right but I could hear him (Mr Keys) yelling and we were all in the water. As I was going down everything just flashed before my eyes."
Quick thinking employees of Coomera Houseboat Holidays -- at the end of Shipper Road in Coomera -- used a tinnie to rescue the men within minutes.
Mr Davies was the taken to Gold Coast Hospital with back injuries after being pinned under the fence. Mr Donnelly was treated at the scene for leg injuries.
Mr Donnelly, Mr Willans and Mr Davies -- all from Ipswich -- had just returned from a week-long house boat trip with Mr Keys, who is from Tasmania.
Mr Keys had been standing with the men but said by some piece of strange luck he had not fallen in the water.
"When it went down I just thought (expletive), it was terrifying to watch and initially I thought it was just the fence," he said.
"Mick didn't come up and I was just yelling 'Where's Mick? Where's Mick?' They were a fair way out and as soon as it happened everyone raced out."
The Ownership Group, which owns the land, yesterday released a statement calling the accident 'unfortunate' and said an investigation was under way.
The statement said the group would 'take every step to determine the cause of the accident, which may have been related to recent rains'.
A witness who did not want to be named was standing on the other side of the river and said he just happened to be looking in the right place at the right time when the concrete collapsed.
"I just happened to look across the water when I saw it happen," he said.
"Three blokes were standing at the rail and it just collapsed and they all fell straight on to the jagged rocks and into the water. The structure just let go."
Police were not called.