Trains between Workington and Carlisle will be cancelled for at least six weeks.
During a recent inspection, Network Rail engineers found the base of two supporting pillars of the railway viaduct over the River Derwent in Workington have begun to erode.
An unusually wet February resulted in fast flowing water along the river, which has damaged the pillar and riverbed.
Engineers have begun emergency repair work and Network Rail said due to the complex environment, the work is expected to take at least six weeks.
Because the river is tidal, engineers can only safely carry out repair work when the tide is out.
Network Rail said the repair work was necessary to prevent further deterioration of the pillars. Without intervention, this could cause the pillars to fail and, eventually, the viaduct to collapse, it added. Network Rail has closed the viaduct to all rail services.
Phil James, North West route director, said: “Climate change is often viewed as a future problem but it’s already causing more frequent and more severe extreme weather events. We are now seeing the impact with more issues like the erosion of this railway viaduct over the River Derwent.
“I’m really sorry that passengers travelling to and from Workington are inconvenienced while we carry out this emergency work. The repairs will take longer than usual as we are only able to work while the tide is out.
“Our engineers are currently on site with our contractors and work has already started on the repairs.”
During the work, no trains can pass over the viaduct. Passengers are advised to check https://www.northernrailway.co.uk/service-updates for the latest information.
Craig Harrop, regional director for Northern, said: “We have a rail replacement bus service in operation between Workington and Carlisle to ensure our customers can get to their destination whilst this essential work is completed.”
