Daily flows down the Murray River are predicted to reach levels not seen in nearly 50 years.
The updated forecast comes after recent flooding inundated some shacks and low-lying areas in the Riverland this week.
Emergency services said up to 120 gigalitres a day would flow down the river by early December.
The new forecast flows are an increase of 30 gigalitres a day, with the flooding emergency in Victoria behind the recalculation.
That prediction will see South Australian government engineers and flood planners check key levees along the river to ensure they can withstand the predicted flows.
Premier Peter Malinauskas said time was "on our side" but "we do need to start getting ready".
"The information that we have at hand doesn't suggest that major towns are going to be inundated with major flood events," Mr Malinauskas said.
"We are advised that South Australia does face the prospect of more water coming down the River Murray than what we've seen since 1975.
"Levee systems will be potentially tested and we do need to be getting prepared where we can."
He said the Renmark levee would handle up to 130 gigalitres of water a day, but some areas of concern would be checked and any upgrade works undertaken if needed with the help of the State Emergency Service.
State Emergency Service Chief Officer Chris Beattie said "mixed ownership" of the levees between the state government, local councils and private operators had created inconsistencies in the maintenance of them.
"That's [the condition of the levees] are something we're turning our attention to," Mr Beattie said.
"This is not about a major piece of infrastructure work, it's about identifying those areas of concern and shoring them up ... with engineering support".
Despite the forecast he said people should still enjoy the Riverland but be extra vigilant.
"With the heightened water flows, there's a change in the velocity and it can be flowing quite quickly and we do see an increase in the vegetation that gets caught up on the riverbank," Mr Beattie said.
Outback drenched
In the state's north, the Olympic Dam Highway has reopend between Pimba and Woomera after earlier being closed due to localised flooding.
The same stretch of road had to be repaired earlier this year after it was washed away.
Yorkeys Crossing near Port Augusta, the Oodnadatta Track from Marree to Oodnadatta and the Birdsville Track from Mungeranie to Marree are also closed due to flooding.
The Barrier Highway, which connects Broken Hill to Wilcannia, has been closed due to flooding.
