The black fence has been installed across the old train tracks and siding at the heritage listed Metropolitan Tunnel in Helensburgh on Friday, with a gate still to be installed.

The Mercury understands Crown Lands - who have ownership of the land - are responsible, with the purpose to restrict public access to curb vandalism and deterioration of the glowworm population.

Helensburgh Landcare spokesman Allan House said the group, who look after the environment of the area, together with local residents met with Crown Lands officers to discuss how to manage the site.

“We’re forever tidying up people’s mess, the glowworm population has just been decimated by the flares and fireworks as people make what think are very clever photographs but are very detrimental to that insect,” he said. 

“It has just become a disaster.”

Mr House was part of the original excavation group who dug out “40 truck loads” of soil and rubble in 1995 to reveal the historic site.

“If I’d known what was going to happen … I would never have allowed the excavation to go ahead,” he said.

Read more: 50 July school holiday activities you’ll really want to know about

The 130-year-old wooden sign has also been taken down after repeated attacks by vandals.

Once the gate is installed with the fence the tunnel will be barred to public access for some time while the glowworm population recovers, according to Mr House. It will then be open for public access at certain times, most likely weekends, in a bid to manage the number of visitors.

“I don’t think anybody is really saying there will be no access it’s just got to be controlled access,” Mr House said.

Hundreds of people were venting their outrage via a number of Facebook groups and pages.

“The masses destroying such places ruining it for everyone,” posted Damien Mountain Woods on the to Australian Landscape Photographers group.

“Are you kidding? That’s ridiculous. Nothing for free,” wrote Steven Jenner to Lost Wollongong & Yesterday Stories.

“CCTV would of cost less than that fence if u wanted to stop vandalism ... they will gain access if they want to u twits, no different to tagging trains,” wrote Jerry Harriman on Northern Illawarra.

Crown Lands has been contacted for official comment but are yet to respond.

The Sutherland to Wollongong train line was built between 1884 and 1886 to service the region’s coalfields and farms. There are seven tunnels between Waterfall and Otford, collectively known as the Helensburgh Tunnels.

The tunnels were abandoned by 1920 when the railway was realigned, with the Otford tunnel later used as a mushroom farm.

The tunnel is the fourth on the original Illawarra line houses a colony of glowworms which can be seen shining from the ceiling like a constellation.

It’s also the location for the popular ghost tours searching for the spirit of miner Robert Hales, who was hit by a train in the tunnel in 1895, cleaving his body in two.

Legend has it the miner’s ghost still hides in the darkness.