Trains into London Waterloo are being delayed this morning because of fallen leaves on the tracks.
Congestion is being caused by leaf-fall coating the top surface of the rails, National Rail said.
"As a result, services operate at reduced speed through affected areas, causing minor delays. This is mainly affecting services between London Waterloo and Surbiton," the rail operator said.
Train services running to and from these stations may be delayed by up to 10 minutes or running non-stop, with disruption expected until 10:30am.
"During peak times even minor delays can cause further knock-on delays to other services," National Rail said.
"These knock-on delays have led to congestion forming on the approaches to London Waterloo this morning. The congestion is affecting services both into and out of London Waterloo, with affected services experiencing delays of up to 10 minutes."
Meanwhile, trains between Stevenage and London Kings Cross/Moorgate are subject to delays of up to 15 minutes due to a failure of the electricity supply earlier today between Stevenage and Moorgate. The disruption is expected to continue until 10:30am.