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Marty Black called the activity ''ridiculous'' after being contacted by a local father, who was concerned about his son and a group of youths jumping into the river.
''In the strongest terms it's ridiculous how dangerous it is.
''They need to grow up and get some brains,'' Mr Black said.
As well as the obvious dangers of jumping from that height (about 10m), the number of boat users on the river meant the potential for serious injury or death ''doesn't bear thinking about'', he said.
''To be blunt, it's bloody stupid.''
He said people also jump off the Albert Town Bridge, but while still risky, it was not as high as the Kawarau Bridge.
Mr Black has been in touch with the NZ Transport Agency, who he said was concerned about the young people's behaviour.
The issue had also been reported to resort police, and Sergeant Blair Duffy urged parents to keep an eye on their children.
''There are certainly risks involved, the height of the bridge, and the strong current, coupled with rocks,'' he said.
Sgt Duffy said anyone who saw people jumping off the bridge should contact police immediately.
The $22million, two-lane bridge opened in May.