Those at Tallowa dam witnessed amazing sights on Monday as the dam broke its banks and hundreds of gigalitres (one gigalitre is a billion litres) topped over.
The equivalent of 20 years worth of the Shoalhaven's water supply flooded over Tallowa Dam's banks in the space of 24 hours.
In his 25 years at Shoalhaven Water, acting director Robert Horner said he had never seen an event like this.
"Tallowa Dam reached a peak water level of 3.3 metres over the top of Tallowa Dam which equates to around 350 gigalitres of water," Mr Horner said.
"Tallowa Dam actually hold about 90 gigalitres, so it was more than the dam itself."
Mr Horner reassured the community that there would be no effect on drinking water.
"The reason there is no effect is because we pump from the Shoalhaven River downstream of Tallowa Dam at Burrier up into an upstream storage at Bamarang and Bamarang Dam has no river systems, creeks or tributaries flowing into it.
"That dam is full at the moment, so we have a buffer period where we just use water from Bamarang Dam, we won't need to pump from the Shoalhaven River for a number of weeks."
The recent floods had caused inundation of roughly 30 of Shoalhaven City Council's 230 sewerage pump stations.
"All of our systems are up and running as normal now except for one pumping station in Shoalhaven Heads that our guys are working on.
"Basically due to the remaining high level in the Shoalhaven River."
Over the past two weeks Sussex Inlet received the highest downpoor with 970mm recorded but most areas, particuarly in the northern Shoalhaven, received more than 500mm of rain.