Raw sewage is spilling into the Harts River in Vryburg in the North West, civil rights group AfriForum said on Monday.
Chairman Herman Swanepoel said the problem had been going on for six months.
"Members of the community have inspected the sewage works and nothing has changed. Raw sewage is still passing through the plant and being discharged into the Harts River.
"The [Naledi] municipality assured us that the problem will be resolved by March 15, but this is not the case," said Swanepoel.
"Our constitutional rights are being violated and in terms of the National Water Act, polluting the country's water resources is a criminal offence," he said.
The Naledi local municipality was not available for comment.