The Maritime Union of Australia has concerns the unlit Cliff Head oil platform could put mariners safety at risk. (ABC Midwest and Wheatbelt: Chris Lewis)
The Maritime Union of Australia is concerned for mariners' safety now the Cliff Head oil platform's lights were turned off.
Operators of the platform called in administrators in July.
Marine Safety WA urges mariners to be aware of the navigation hazard.
An abandoned oil drilling rig rusting away at sea is raising safety concerns now the platform's lights are no longer working.
The Cliff Head oil platform has been at the centre of a storm over who foots the $200 million clean-up bill after junior oil and gas companies Pilot Energy and Triangle Energy entered voluntary administration.
Pilot was working with Triangle to repurpose the rig but in July both companies went bust.
Now sitting idle 11 kilometres off the coast of Dongara, about 350 kilometres north of Perth, the rig which has been used as a navigation aid for more than a decade remains unlit.
The stretch of water where the old drilling rig sits is frequented by mariners including commercial fishermen.
Western Australia's Department of Transport and Major Infrastructure released an alert about the lack of lighting on the oil rig.
Marine Safety WA has advised all mariners in Dongara and Leeman waters to be aware of the 500-metre exclusion zone surrounding the site and to check navigation warnings.
Thomas Mayo says the unlit platform is very dangerous. (ABC News: Michael Franchi)
Maritime Union of Australia assistant national secretary Thomas Mayo said unlit infrastructure out at sea could be a "huge risk for mariners" at night.
"It's very dark out there, you don't have street lights or anything like that [in the ocean]," he said.
"You've got all sorts of weather and conditions to contend with so it's extremely dangerous to have a facility out there unlit.