The road across the top of the Hume Dam will be closed to foot traffic from August 26 for the next two years for maintenance works.
The scheduled maintenance will include mechanical, electrical and restoration upgrades and will continue until 2021.
WaterNSW said for safety reasons the crest roadway will be closed throughout the project with no public access.
Gates will be locked either side of the spillway and signs will be in place.
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The public road between Hume Dam Village and the dam may also be closed at times so large equipment can be moved to and from the dam wall.
"Fishing and boating will not be allowed within the restricted zone upstream of the dam wall at any time during the work as diving activities will be undertaken," a spokesman said.
"We understand there could be some inconvenience during this work and are seeking cooperation from the community as the upgrades are completed."