A one-in-1000 flood around the Hawkesbury Nepean, such as that in Queensland early last year, would cause up to $8 billion in total damages affecting 14,000 homes and requires urgent preventative measures, according to a group of 10 western Sydney councils.

A one in 1000 flood is one that has a 0.1 per cent chance of happening each year.

The Western Sydney Regional Organisation of Councils last night called on the state government urgently to  address threats of potential floods around the Hawkesbury Nepean.

A repeat of the 1867 flood would cause up to $1.7 billion in direct damages and $3 billion in total damages, the group said.

"This would affect an estimated 7600 homes, with about 1200 of those destroyed, WSROC president Tony Hadchiti said.

Flood prevention measures could include raising the wall of the Warragamba Dam, which filled to capacity in March, spilling water over the wall.

Infrastructure NSW last month backed the implementation of Hawkesbury Nepean Flood Plain mitigation measures as a key recommendation of its 20-year strategy "First Things First".

Cr Hadchiti said the flooding was a serious concern for key western Sydney councils including Liverpool, Penrith, Blacktown and Hawkesbury.

"Our councils have been calling for action on this issue for years," he said.

A study carried out as part of the strategy had shown there were 21,000 residential buildings on the floodplain – 5000 more than previously thought, and that an additional 143 hectares of commercial and industrial property had been built since 1990, he said.

He said: "A flood of this magnitude would put 43,000 residents and 9000 employees of local business at risk.

"These are risks that we simply cannot afford to take and the NSW government needs to act on these recommendations as a matter of urgency."

The issue was also raised at last week's Local Government and Shires Associations conference in Dubbo with calls to both the NSW and federal governments for a study to determine the potential threat.

WSROC vice-president, Tiffany Tree, who is also the deputy mayor of Hawkesbury, said she strongly supported the need for action to fund key mitigation initiatives such as raising the dam wall.

"This is important because, although individual councils have conducted their own studies, we need an overall regional assessment in order to be truly effective,'' she said.

In his book Hawkesbury Heritage, Stan Stevens wrote that the 1867 flood "from Riverstone to the Blue Mountains, and from Pitt Town to Kurrajong extended a vast inland sea dotted only by the islands of Windsor, Richmond and Pitt Town.

"Many residents of the Lowlands, as they were being taken to safety, watched heartbroken as uprooted trees, broken furniture and other debris smashed into their homes, pounding against walls and even caused some buildings to be swept off their foundations."

Residents all over the Hawkesbury, clinging to roofs of their homes, fired gunshots to alert rescuers in boats to their location, he said.