"There is always a bit of a risk because it is not the same quality as tap water which is safe for drinking.
"But the water is of acceptable quality for swimming and we test the water twice a week," Francois van Wyk, spokesperson for Rand Water said on Sunday.
Van Wyk said that there had been ongoing complaints in the Vereeniging area.
He said residents along the river gathered on Tuesday to air their complaints and fears about water pollution.
Members of the media and the municipality were also present.
"Despite infrequent pollution incidents, the water holds minimal risk for swimmers" said Van Wyk.
The annual Emerald Challenge is hosted along Emerald Casino Resort's Vaal River front in Vanderbijlpark.
Rand Water was contacted by the casino after reports of pollution surfaced.
The challenge is due to be held on December 1.