An unexploded Second World War bomb has been found in the River Thames, close to the starting point of Sunday's annual Oxford-Cambridge boat races.
The device was spotted near Putney Bridge by a member of the public, who called the police.
The race starts just metres away from the spot and thousands of people are expected to converge on the Thames for the event on Sunday.
A Scotland Yard spokesman said: "Police were called by a member of the public at approximately 1.50pm on Saturday reporting what they thought to be World War Two ordnance on the Chelsea shoreline by Putney Bridge.
"Officers including the Marine Policing Unit attended. The item is currently submerged."
Race organisers are currently planning on continuing with the event as anticipated but are working with police.
They said any decision made would be done in conjunction with the authorities and would not be made on Saturday.
The men's event has been running for 163 years and will begin on Sunday at 5.35pm.
The women's race is in its 72nd year and will start at 4.35pm.