A man dived off London's historic Tower Bridge into the River Thames on Monday during a protest by taxi drivers over their exclusion from part of a special Olympic Games road network in the capital.
Police pulled the man from the water under the landmark bridge, from which Olympic rings were suspended to celebrate the 2012 London Games, and arrested him on a public order offence.
The Port of London Authority said the man, thought to be a taxi driver, was lucky to be alive after diving headfirst from the walkway about 8 metres (25 feet) above the water.
"This was an absolutely crazy thing to do. He could easily have killed himself," the spokesman said. "He has tied up a lot of resources and endangered others."
The man, who has not been named, had been taking part in a protest by London taxi drivers over a decision to keep them off part of a road network reserved for Olympic athletes, officials and journalists.
On a rare hot summer's day in the capital, several hundred black London taxi cabs inched along the bridge hooting their horns close to London Mayor Boris Johnson's office. The drivers are worried that they will be stuck in congestion and will lose money during the Games.
London's 25,000 taxi drivers want access to all sections of the temporary network. Black taxis are currently only allowed in two thirds of the 100 mile (160 km) route.
The United Cabbies Group, which organised the bridge protest, said it did not "condone or recommend jumping in the Thames".
"He climbed on the bridge and threw his keys at the onrushing police before jumping in," the pressure group said on its Twitter page. A spokesman for the group could not immediately be reached.
The chairman of the RMT London taxi union, Mick Bailey, who was at Tower Bridge supporting the protest, said: "There are still 25,000 cabs that can't do their jobs properly because of all the restrictions and the failure to allow us to use the Olympic Route Network".
Police and the military have increased patrols on the Thames as part of Britain's biggest peacetime security operation.
Tower Bridge, which opened in 1894, is one of London's best known landmarks. Its roadway can be raised to allow tall ships to pass through.