The boat ramp next to Tonkin Oval, Cronulla, is being replaced at a cost of $1.57 million.
The facility will remain single trailer width, but a new pontoon for launching small craft in Gunnamatta Bay will be added.
The existing ramp was due to be closed today (May 27) and the work completed by October 31 this year.
Works will take place weekdays from 7am-6pm and Saturdays from 7am-4pm.
The car park will remain open during the upgrade, although some minor asphalt resurfacing will be carried out.
Sutherland Shire Council and the state government are jointly funding the project, which has proved to be more costly than originally anticipated.
In 2015, the state government announced a grant of $250,000 towards the work, which then Minister for Roads and Freight Duncan Gay said would meet present and future demand.
Cronulla MP Mark Speakman said at the time Transport for NSW and Roads and Maritime Services would work with the council to finalise the scope of the project.
''I anticipate some council funding will be required, but not necessarily anywhere near matching funding,'' he said.
A council spokeswoman said this week the upgrade of the facillity was "an exciting waterways project that will enable the local community, as well as visitors to Sutherland Shire, to continue enjoying a range of activities on the Port Hacking".
"The works will improve access and safety and will include the construction of a new boat ramp, a pontoon with a step to launch small craft and minor asphalt resurfacing of the adjoining carpark.
"The project is expected to be complete by summer."
The spokeswoman said, until the project was completed, the closest alternative boat ramps were Water Street Caringbah, Wally's Wharf Dolans Bay, Wonga Road Yowie Bay and Swallow Rock Drive Grays Point.
"We apologise for any inconvenience the upgrade works may cause," she said.
Stage two of the project, consisting of reconfiguration of the car parking area, is subject to funding being provided and approvals.