Wallaga Lake Bridge is undergoing maintenance work to repair and strengthen the structure after delays caused by bushfires and flooding.
Transport for NSW Regional Director Southern, Jo Parrott, said this work is the second stage of repairs on the bridge after new piles were installed last year.
"Transport for NSW will now repair the deteriorated sections of the bridge deck and install new steel support structures," Ms Parrott said.
"Wallaga Lake is the largest lake in southern NSW and the bridge is an important piece of local infrastructure which has been in operation since 1834.
"The bridge is currently safe to use but the upcoming repair work will ensure it remains safe for all road users well into the future.
"Every effort has been made to ensure continued access for traffic while the work takes place and the bridge will remain open for the majority of this work.
"In the event of an emergency, the worksite can be packed up at short notice and the bridge can be immediately opened to traffic."
Work is being carried out between 7am and 6pm on weekdays with work expecting to take up to four weeks, weather permitting.
The bridge will be closed daily between 8.30am and 3.30pm weekdays with a detour in place via the Princes Highway to Cobargo and then the Bermagui-Cobargo Road to Bermagui.
Traffic control and a reduced speed limit of 40 km/h will be in place at all times on Wallaga Lake Road for the duration of the work.
Motorists are advised to plan their journeys, allow an additional 30 minutes travel time, drive to the conditions and follow the directions of signs and traffic control.
Transport for NSW thanks the community for its patience while work is carried out.
For the latest traffic updates call 132 701, visit livetraffic.com or download the Live Traffic NSW App.