A girl fell off a carnival float and was run over by a lorry after spectators fired a water pistol at her.
Furious organisers have condemned the "idiots" who caused the accident, which left the 12-year-old with a broken arm.
It is believed the youngster ducked to avoid somebody firing a water pistol from the crowd, lost her balance and fell about 8ft into the road.
Ron Noakes, chairman of Worthing Rotary Carnival's organising committee, said the low-loader lorry then ran over her arm in front of spectators.
The girl was on the Stray Cats Youth Club float in Marine Parade, just east of West Buildings, when the incident happened.
Mr Noakes said the carnival princess, 12-year-old Jessica Hunt, riding in an open-topped Mercedes car, was also soaked by water balloons.
Mr Noakes said: "Things went tremendously well until these incidents. We understand a girl aged about 12 fell off a float and broke her arm. I understand there were these idiots with water pistols and water bombs.
"Apparently she was trying to duck out of the way of the water and fell off the float and the lorry went over her arm and broke it.
"We are disappointed and very concerned for the girl. That is one of the reasons we insist every float is insured."
Mr Noakes believed the culprits were three men and a woman aged between 25 and 30.
He said: "We have got the details of a person who saw everything that happened and is prepared to make a statement to the police."
The Stray Cats Youth Club is based in Ham Road, East Worthing, and enters a float every year. Nobody was available for comment today.
On a brighter note, Mr Noakes said the carnival would raise about £10,000 for worthy causes.
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