The North and South Bank of the Serpentine, Hyde Park are currently closed due to the discovery of suspected World War Two ordnance, the police informed the public.
"Apologies for the inconvenience this causes, officers are on scene and investigating," London police service added.
The part of the park suspected to contain the bomb, has been cordoned, with large police presence at the scene — between the Triangle car park and the boat house on Serpentine Road.
A witness reportedly said they heard a confirmation of a bomb disposal experts on the way to the park.
"Police were frantically putting up some barriers, so I asked what was going on," an onlooker reportedly told the media.
He added that maintenance workers were came across a large shiny object at the park, which turned out to be a 14ft long bomb.
A statement from the Royal Parks, a charity that manages London's eight Royal Parks, said:
"We can confirm that a suspicious object, probably an unexploded WW2 bomb, has been found in the Serpentine Lake in Hyde Park. Specialist police officers are on the scene and a cordon is currently in place between the Triangle car park and the boat house on Serpentine Road."