The theft of a pipe has caused a crude oil spill in the Bellair area, in Durban, affecting the Umbilo river.
The river flows into the Durban Harbour.
The extent of the environmental impact will be assessed by MEC for Economic Development, Tourism and Environmental Affairs Nomusa Dube-Ncube.
"I have assigned a team of environmentalists from my department to work with Transnet following a pipeline theft incident that resulted in the spillage of crude oil," Dube-Ncube said.
"We are working with all role-players to implement spill containment measures to prevent damage to the environment."
Transnet operates and maintains a network of 3 800 km of high-pressure petroleum and gas pipelines from Durban to Gauteng, which stretch across five provinces.
They have recorded over 80 incidents of fuel theft and of attempted theft.
They have also recorded cases of tampering with pipeline infrastructure, with the intention to steal fuel, said Dube-Ncube.
"We are calling on communities to work with law enforcement agencies to ensure that those who are responsible for vandalising Transnet pipelines are brought to book."
Clean-up operations will include the source of the spill, as well as the harbour.