Cliefden Caves have been granted state heritage listing, almost certainly sparing them from the Cranky Rock dam proposed for the region.
The caves, located on private land between Blayney and Canowindra, are known for their Ordovician-era fossils dating back about 460 million years.
The listing covers about 1550 hectares.
Graham Quint, director of advocacy for the NSW division of the National Trust of Australia welcomed this week’s formal gazetting of the karst cave network on the state's register.
“[It is] the highest level of protection you can have in NSW – it can't be destroyed,” he said.
“It's just a really silly area to build a dam.
“No one knows where the limestone ends up – so it's probably not a good place to put [one],” he said.
The Coalition government has been examining options for a dam in the area, with one proposed for the Cranky Rock area over the Belubula River nearby.
A spokesman for WaterNSW said it was “currently evaluating potential solutions aimed at improving water security in that region.
“The environment and the significance of the caves have always been important considerations in any analysis of potential water security infrastructure options,” he said.
Environment minister Gabrielle Upton said fossils in the caves were recognised internationally.
“It's great to be able to acknowledge the caves' significance,” she said.
Harry Burkitt, secretary of the Save Cliefden Caves Association said it was “fantastic news.”