The Vaal Dam was 103% full and three sluice gates were open, spokesperson Linda Page said in a statement.
It had an outflow of 870m³ per second.
In the Free State the capacity of the Bloemhof Dam was currently at 104% with an outflow of 1 000m³ per second.
The Gariep Dam, the largest dam in South Africa, was at 107% with an outflow of 1 670m³ per second which would increase to about 2 900m³ per second, Page said.
The capacity of the second largest dam, the Vanderkloof Dam, was at 107.7% with an outflow of 1 323m³ per second and would increase to about 2 500m³ per second.
As more rain was forecast over the next 24 hours, it was expected that changes to outflows would be made, she said.
“The department of water affairs wishes to again urge all communities to exercise caution in the vicinity of the Vaal Orange River System and affected dams,” Page said.