A second peak in Murray River flows through South Australia is likely to hit 185 gigalitres a day in late December, with thousands of properties set to be flooded.
Latest modelling has river flows rising to 175GL a day early next month, before a period when the water level will settle.
However, a second peak will hit around Christmas after recent rains interstate and the release of water from the Hume Dam.
Premier Peter Malinauskas said to put that in perspective, the flows would be close to the total amount of water consumed by all South Australians over a full year.
"We now face the prospect of that coming across the border every single day," he said on Thursday.
"It's a lot of water. It presents a lot of challenges."
The flooding down the Murray is expected to be the worst since the 1970s, with more than 4000 properties including shacks, homes and businesses likely to be inundated.
River flows on Thursday were sitting at about 129 GL, but were steadily rising.
Areas most at risk include Renmark, near the Victorian border, and Mannum, east of Adelaide, where a levee may be built down the main street, potentially stranding some homes and shops on the wrong side of the barrier.
Some have already begun moving out stock and personal items and preparing for their properties to be inundated.
Earlier this week the state government unveiled a $51.6 million assistance package for property owners impacted by the rising water.
The money will fund levee construction and repairs, support tourism and other businesses, and provide assistance to homeowners.
It includes $9.3 million for levee works, $4.8 million for sandbags and other defences, rental assistance for families, grants of up to $20,000 for businesses forced to close, and grants to buy generators for properties set to lose power.
The government has also set aside $1 million for mental health support, $3 million for vouchers to encourage tourists to continue to visit the region, and $10 million for infrastructure repairs, including roads.
Individuals will be able to apply for $400 personal hardships grants, with families to receive $1000.
South Australia will on Thursday take delivery of four kilometres of flood barriers from Italy, and expects an extra 400,000 sandbags to arrive in the coming days. The premier described such resources as a "hot commodity" at the moment.
The looming floods have prompted calls from the Australian Medical Association for officials to be mindful of the health impacts, with road closures potentially preventing locals from accessing medical treatment and a possible increase in mosquito-borne diseases.
'We ask that those in charge of preparing and managing the response in the Riverland consider health services as among those necessary during the emergency and for the weeks of recovery," AMA state president Michelle Atchison said.
Dr Atchison said if people congregated in relief centres, the risk of a COVID-19 outbreak would also increase, adding to the number of people seeking medical help in "extremely fraught conditions".
'With peak flows set to remain high well into January, residents and visitors should fill scripts and replenish supplies of repellent, masks, rapid antigen tests and other health essentials now," she said.
"Please don't wait until access is cut off."
Mr Malinauskas said SA Health was already working on the provision of key vaccines across river communities, including the one for the potentially deadly Japanese encephalitis.