A FATHER says he is preparing himself for the worst after his 20-year-old son was involved in a fatal jet-ski accident during a dream holiday in Hawaii.

Carpet cleaner Tyson Dagley, of Crestmead, south of Brisbane, is in custody in Honolulu and faces up to a year in jail after being charged with third-degree negligent homicide.

Hawaiian police allege Dagley was standing on the jet-ski and not paying attention to where he was going when he smashed into another jet-ski being ridden by Californian teenager Kristen Fonseca on Keehi Lagoon.

Ms Fonseca, 16, died of a brain injury after apparently hitting her head on the steering wheel of her jet-ski.

Although the crime is a misdemeanour, a judge set a $100,000 bond because Dagley was considered a flight risk.

Dagley's girlfriend, Natasha Ryan, was charged with hindering police after allegedly deleting video of the incident, but has been released on a $500 bond.

Mr Dagley's distraught father Alan told The Courier-Mail from a Hawaiian hotel room yesterday that he feared his son would not return home with him.

"The maximum penalty is a year in jail, so we're trying to prepare ourselves for the worst and go from there," he said.

"We know they (the victim's family) are hurting and we couldn't imagine being on their side. Tyson was saying to us that he wished it was him."

Mr Dagley said the young couple had been saving for nearly two years for the holiday. "Tyson and Natasha had been saving very well to do this (the holiday) all by themselves," he said.

"He's very scared, he's still not that well with the injuries he got through his neck, head and shoulders. He's a good kid, he hasn't got a bad bone in his body, he wouldn't hurt anyone and that's the honest truth, he's so kind-hearted and accidents happen."

Ms Ryan, who attended St Thomas More College at Sunnybank, declined to be interviewed.

Speaking from Brisbane, her mother Susan said she was devastated by the loss suffered by the Fonsecas, but also devastated for her daughter and her boyfriend.

"He's a wonderful kid and Natasha is the most big-hearted child," she said.

US media reported Ms Fonseca's stepfather Mario Canton told police Dagley's jet ski was travelling about 35-40mph (56-64km/h) when it hit his daughter, who was moving slowly.

Dagley, who wore a neck brace in court, will return to court on Tuesday to enter a plea and for a ruling as to whether a jury will hear his case. Ms Ryan is due back in court in September.