A railway line closed for urgent works to stop subsidence will not reopen on time due to the discovery of "more complex issues with drainage".
Part of the line between Manchester and Sheffield closed completely in June after previously being hit by closures and cancellations from an earlier landslip.
The section of the railway was supposed to reopen on 25 August but Network Rail bosses are now pushing the date back to 23 September.
They said engineering work to stabilise the earth led them to find further repairs were needed, causing a four-week delay.
A bus replacement service is in place between Sheffield and Manchester Piccadilly and there will be changes to timetables due to the ongoing works in Hague Bar, New Mills, Derbyshire.
Network Rail said five state-of-the-art drainage chambers will be required to be built under the railway to collect excess water and direct it to the River Goyt.
These chambers are expected to last for 120 years, and will mean the railway is more resilient to climate change, they said.
A Network Rail spokesman said the works will be carried out as "quickly and efficiently as possible to minimise disruption to the community".
'Sorry for disruption'
The work means there will be some changes in services from Manchester to New Mills Central via Bredbury.
From Monday to Saturday there will be an hourly train service between Manchester Piccadilly and Marple.
On Sundays, an hourly bus service will run between Manchester Piccadilly, Bredbury, Marple and Chinley.
Services between Chinley and Manchester Piccadilly continue to divert via Hazel Grove and Stockport, with a bus service between Chinley and Marple.
Vitesh Solanki, Network Rail’s scheme project manager, said: “I’m sorry for the disruption the rail closure will cause passengers.
"We have received a tremendous welcome from the community in New Mills and we are grateful for your patience while we carry out this important work.”
Network Rail is holding a meeting for residents on 29 August from 19:00 BST to 21:00 BST at New Mills Town Hall, regarding the works.
