CBBC presenter Holly Walsh had to be rescued by a lifeboat after she took part in the annual Worthing International Birdman competition.
Holly was strapped to a spinal board after being rescued from the water by divers and was taken to hospital with a suspected dislocated shoulder and fractured arm.
She had jumped off the pier and plunged into the water in a mock helicopter in aid of The Rainbows Children Hospice.
Shoreham lifeboat spokesman Dave Cassan, said: "We can confirm we were tasked to get a person out of the water. It appears she entered the water wrong.
"It is thought she has a serious fracture above her elbow and a dislocated shoulder. The inshore lifeboat brought her to the shore at Worthing and she was transferred to hospital by ambulance."
The contest was halted for about 20 minutes while she was rescued.
Around 10,000 spectators were believed to have attended the second day of the two-day event, where so-called "fun flyers" dress up in elaborate costumes and attempt to "fly" the furthest off the West Sussex town's pier.