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''This practice is dangerous and will no doubt cost someone their life should it continue,'' Sergeant Derek Ealson, of Alexandra, said.
The Clyde boy was ''joking around'' with friends at the bridge on Monday afternoon when he jumped into the river from the bridge's highest point.
The distance was later estimated to be about 30m.
A concerned member of the public contacted police.
Officers went to the site but the boy was fine and did not require any medical treatment, Sgt Ealson said.
''There were several dangerous elements - the distance he fell, the swiftness of the river and the potential to hit his head on rocks under the surface, or be injured on impact with the water.
''It's an inherently dangerous river, in parts, and the police and Coastguard have been involved in a number of rescues of people who have got into trouble after entering the water.''
Climbing up the bridge was also dangerous and placed motorists at risk as well. Teenagers had also been seen recently jumping into the Clutha River from the Alexandra bridge and Deadman's Point bridge at Cromwell. Those activities were also dangerous, Sgt Ealson said.