Rising water at the Vaal Dam has officials considering opening a further sluice gate to ease capacity.
This will increase the flow of water into the Vaal River and the danger of flooding downstream.
On Tuesday morning, acting director-general of Water Affairs Trevor Balzer told Talk Radio 702 they were considering opening the eighth gate at the Vaal Dam.
The gates were already discharging more than 940 cubic metres into the Vaal River and the opening of another gate could burst the riverbanks, Balzer said.
He said the Bloemhof Dam, in North West, on the Vaal River, was at 80 percent capacity and emergency services had been warned about flooding.
Meanwhile, disaster was narrowly avoided on Tuesday morning when a truck almost tipped off a bridge on to traffic on the N12 near Edenvale. The back end of the truck could be seen dangling off the bridge on the R24 west.
The driver sustained minor injuries.
On Monday, e-tolling critics said alternative routes were deteriorating and potholes were increasing as people tried to avoid the toll roads.
Gauteng residents were likely to see more rain until at least Friday, said Elizabeth Webster, a forecaster at the SA Weather Service.
Six people have drowned in various parts of Mpumalanga so far because of the flooding and a man who fell into the Crocodile River in Schagen, Nelspruit on Friday is still missing.
The Kruger National Park’s bush camps remain closed.