Rail passengers are facing delays along the Brighton mainline due to flooding and there could be worse to come.
A signalling problem caused by flooding has mean delays of up to 15 minutes between Haywards Heath and Brighton.
The flooding is in Patcham, where groundwater levels are rising following the recent heavy rain.
Southern Rail has said there is a high risk of groundwater flooding, which would mean the line would have to close.
Were this the case, all trains would have to be diverted via Lewes, which would cause large delays.
Network Rail and Southern are working together with the Environment Agency to keep track of water levels in Sussex over the next few days of bad weather.
Over the next few days, they aim to provide progress updates on the areas of anticipated risk.
Passengers are being asked to check before they travel.