A pedestrian underpass is to be turned into an emergency pond to hold hundreds of thousands of litres of floodwater threatening homes and businesses in south London.
The Purley Cross underpass will be used to hold water pumped from around 400 under-threat buildings in parts of Kenley and Purley and to stop a water treatment works which supplies tens of thousands of homes from flooding, Croydon Council said.
The authority said the plan to use the underground footway to hold around 600,000 litres of water from tonight was approved after its "primary" pond at Purley Depot overflowed last night.
The local situation continues to worsen and more heavy rain is forecast.
The underpass act as a secondary "balancing" pond, allowing the emergency services and council engineers to pump water quickly away from the worst affected vulnerable areas and take pressure out of the water system, the council said.
Council leader Mike Fisher said: "This has not been an easy decision to take but it has become increasingly clear over the past few hours that we have no alternative if we are to protect people's homes and businesses from being flooded."
The decision was taken jointly by Croydon Council, neighbouring councils, the Environment Agency, emergency services, Thames Water and Transport for London.
The Kenley water treatment works has also been surrounded by sandbags in an attempt to hold back the floodwater. The plant supplies water to more than 46,000 properties and 116,000 people.
Croydon Council declared a major incident in parts of the London Borough's south on Thursday.
It said officials had visited local residents and businesses which face potentially being affected by the rising water levels and advised them to be prepared.
Information will also be posted online at www.croydon.gov.uk/advice/emergencies/floods.