A contingency plan was in place, the department said in a statement on Sunday.
"The contingency plan is to ensure that the environment and health of marine species in the area are protected," it said.
"At the moment, no oil spill from the vessel has been reported. As part of the contingency plan, containment booms have been deployed around the vessel to protect the coastline against any possible pollution during the salvage operations."
A team of environmental, disaster management agencies and salvage experts were on standby to "boom off the uMlathuze Sanctuary, Richards Bay harbour and near-by estuaries from any possible oil spills".
The MV Smart, a 230-metre-long vessel, was laden with 147 650 tons of coal when it ran aground outside the port in heavy seas on Monday afternoon. The entrance to the port was not blocked.
Twenty-three crew members were airlifted in four sorties from the stricken vessel late Monday afternoon. None of them suffered serious injuries.
On Sunday, the department said its oil spill aerial surveillance aircraft, the Kuswag 9, would continue to fly over the area to gather information that would be used during the salvage operations.
"The aircraft will also assist with monitoring and assessment of any possible environmental threat in the area. The department has also requested samples of the coal on board to determine the impact it may have on the marine environment," the department said.
The uMlathuze Sanctuary was considered important for conservation and social perspectives as a breeding and nursery area for fish species.
"Plans to pump the oil out of the vessel are at an advanced stage. It is anticipated that the removal of oil from the vessel may take anything between five and seven days, while it may take several months to remove the coal.
"Furthermore, it is unclear at this stage as to how long it would take for the stricken vessel to be removed," the department said.
The department, the KwaZulu-Natal agriculture and environmental affairs department, environmental agencies and local authorities were on high alert to provide rapid response in the event of any oil pollution from the vessel. – Sapa