Forecasts have been increased again for water flows down the Murray and into South Australia from the rain in NSW and Victoria with 135 gigalitres a day expected by early December.
Water Minister Susan Close said the predicted surge of water into SA had been revised up from 120 gigalitres last week and could go higher again if rain continues in the eastern states.
The expected high-water event also increases the risk of flooding in SA with the Riverland's system of levees likely to be tested.
Some low-lying shacks, homes, businesses and community infrastructure are expected to be inundated.
Ms Close said the government had allocated $3 million to be distributed to Riverland councils for work to stabilise levee systems including the two of most concern at Renmark as water levels rise to the highest level since the 1970s.
"Many people won't have experienced this in the Riverland or, if they have, it's probably fairly dim in their memories," the minister said.
"So we need to make sure we've got everyone not alarmed, but prepared and alert so that we're able to manage this as smoothly as possible."
Authorities will also ship more sandbags to the region and will conduct a series of community meetings across the Riverland next month.
Inundation maps have been prepared and a River Murray hotline (1800 362 361) set up.
As well as the rising water levels, there is also concern for fish and other animals along the river from an associated blackwater event as organic matter is washed into waterways, lowering oxygen levels.
State Emergency Service Chief Officer Chris Beattie said while most of SA's Riverland towns sat above the Murray floodplain, Renmark is considered the most exposed.
"It's got the most extensive levee system around it. That's where we're putting out attention first," he said.
"But there are other parts across the Riverland where there are levee systems that we'll also be looking at.
"The levees were designed for a 210GL flow event which is what the state experienced in the 1930s.
"At 135GL the levees will be doing their job in terms of holding the river back."
But Mr Beattie said the current modelling was for water "in the system" and couldn't take into account further rain events.
"So it's not beyond the realms of possibility that we continue to see an increase in these forecasts," he said.
