A NPWS spokesman said overcrowding was not a factor on January 26, but that flooding of the weir at Audley had resulted in road closures from 1am until about 9.30am.

"There was no need to instigate the traffic control measures," the spokesman said.

He said the park was only about a quarter full on the day, and no part of it had been closed due to overcrowding.

NPWS had tweaked the Royal's traffic plan ahead of Australia Day after an outcry from Bundeena residents and business people, who claimed it had prevented them from getting home, and transformed their usually busy suburb into a ghost town over Christmas.

Bundeena Service Station owner Mark Douglas said while weather had been a factor, he feared the debacle over Christmas, when motorists were diverted to Waterfall, had discouraged people from heading to the park.

"We feared all along the public's bad experience over Christmas would discourage them from coming back," he said. Electronic signs telling motorists the park would close if full on Australia Day could also have kept numbers down.

"I have never seen it so quiet on Australia Day before," Mr Douglas said.

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