Underground fuel tanks at Wollongong Harbour are being removed before they pollute the waters of Belmore Basin.
The tanks are underground at the stone jetty on the western side of the basin and are being removed by NSW Crown Lands.
"The work is being carried out to remove the potential for pollution from the underground tanks as they naturally deteriorate with time," Crown Lands coastal infrastructure boss Stephen Wills said.
Four tanks and associated fuel lines will be removed. Once used to hold diesel fuel, the tanks are more than 20 years old and the largest has a capacity of 18,500 litres.
"The tanks are empty, although a small residual amount of diesel is anticipated within them and will be removed with the tanks," a Crown Lands spokesman said.
There was little risk of any remaining fuel leaking into the harbour, he said.
"However, additional spill-management measures have been put in place because of the close proximity of the work site to the harbour."
Some odours could be released as the site was excavated but they would be monitored and efforts made to mitigate them, the spokesman said.
While the plan was to remove the tanks, the spokesman said they posed no danger if left in place. In fact, some of the tanks might not be moved at all.
"Some lengths may be sealed with concrete and left in place if removal risks disruption to other services."
During the work, which is to continue through March, there will be short power disruptions and water supplies will be limited.
"Pedestrian and vehicle access is being maintained," the spokesman said.
"Vehicle access may be interrupted for very brief periods during work on sections of the fuel line," the spokesman said.