Flooding in the Murray River threatens to cut off the Princes Highway, south-east of Adelaide, the main road to south-eastern South Australia.
High water levels flowing into Lake Albert could cause the highway to flood in low-lying areas near Meningie.
A speed limit of 60 km/h has been set and there are plans for a detour along Dukes Highway if the Princes Highway is affected by water.
Road concerns grew on Thursday as the spike in river flows reached SA’s Lower Lakes.
That has pushed up the lake’s water levels, with concerns for further flooding of local properties over the weekend as a low-pressure weather system moves through, increasing wave action.
With the high water mark reaching the lakes, Emergency Services Minister Joe Szakacs said this meant the river’s peak had now passed all major communities along the waterway.
“While it’s nice to see the peak edge closer to the ocean, a river-wide flood emergency warning remains in effect in SA and I urge people to remain cautious,” he said.
Further upstream, flows across the South African border have now fallen to about 135 gigalitres per day, down from a high of over 190 GL.
They are expected to fall to about 60 GL per day by the end of January.
So far, most of the state’s levee system has held up, especially those that protect major assets, including one in Renmark, built near the local hospital, and one in Mannum, protecting businesses on the high street.
There have been 68 catastrophic levee breaches and 168 major problems, but most of them involved structures protecting agricultural lands.
The State Emergency Service will continue daily inspections throughout the levee network, with a particular focus on those at Woods Point, Monteith, Jervois and River Glen.
Mr Szakacs said there are still concerns about the integrity of the major levees.
“We are far from out of the woods. These dikes remain under pressure,” he said.
“Small but not insignificant risks remain about scarring, tearing and failure.”