The Trans-Australia Railway across the Nullarbor will remain closed until at least Easter.
The Australian Rail Corporation yesterday (Thursday) said floodwaters between Kalgoorlie and Rawlinna are still delaying the repair efforts.
ARTC says "considerable progress" has been made on track repairs by work crews on "at multiple impacted sites", there are still sections which are flooded.
It had been hoped the critical freight link could be re-opened on Sunday and a further update this week suggested Wednesday as a possible re-opening date.
"Following assessments today, and with water levels not receding at a rate we had hoped for, ARTC advises that the rail line will not open before Easter," the corporation said.
"Until the floodwaters recede, there are still a number of sites with a substantial amount of water over track which cannot be safely accessed to undertake recovery efforts at those locations," ARTC said.
"Continued assessments of the conditions are being undertaken daily with detailed analysis.
"An opening date will be reassessed as conditions change and access to flooded sites becomes available."
ARTC said it now had a "significant workforce" in the remote location since the record rains fell several weeks ago.
Senior engineers, specialist consultants and maintenance crews are working to re-open the crucial freight link from east to west.
Some regions in the arid south-east of WA received their yearly rainfall in just a few days earlier in the month flooding inland areas and closing transport routes.
Triple road trains up to 53.5 metres in length have been approved to help solve the freight crisis across the Nullarbor.
Trucks have been moving across the re-opened Eyre Highway for more than a week now from South Australia to WA but the Trans-Australia Railway remains shut.
The rail network carries the bulk of food and other essential supplies into WA.
The National Heavy Vehicle Regulator last week temporarily approved the crossing of the triple-length road trains over the Nullarbor until the rail network can be repaired.
NHVR chief operations officer Paul Salvati said the notices give consent to increased access for road trains up to 53.5 metres, between Port Augusta in SA and the WA border, and then internally into WA.
Mr Salvati said the notice would provide heavy vehicle drivers and operators with increased flexibility and expedited access to critical routes, facilitating the efficient transport of essential supplies and emergency relief for communities cut off by flooding.
"Truckies have had to take huge detours to reach their destination due to this flooding, and the NHVR recognises the importance of delivering essential items to the affected communities," he said.