As Ivan Maqi, 24, was led into custody from Melbourne's County Court on Friday, some of his family - refugees who fled religious persecution in Iraq in 2000 - and friends cried, wailed and screamed uncontrollably.

Maqi, who killed swimmer Robert Brewster in 2012, was embraced from the dock by numerous people, before being led to the courthouse cells. One woman collapsed and needed to be carried from the court.

Mr Brewster's family, including his two teenage daughters, had quietly left the courtroom earlier.

The court heard Maqi was "hooning, show boating and fanging" his jet ski before he hit Mr Brewster, 51, about 5.50pm on February 24.

Maqi was driving the jet ski in a swimmers' only zone between Lagoon and Kerferd piers off Port Melbourne.

One witness said she saw a jet ski "zooming dangerously close to the pier" and increase speed "closer to the beach".

Another witness estimated Maqi was travelling at 70km/h in the 9km/h zone.

It was the first day he had operated the jet ski.

Prosecutor Gary Hevey told the court Maqi had the Seadoo jetski at "full throttle" as he did spins and went from side to side in the water.

He had a passenger with him at the time.

Maqi, a house painter, pleaded guilty to a charge of culpable driving causing death by negligence - the first time in Victoria such a charge has been laid involving a water craft.

In her sentencing remarks, Judge Sandra Davis noted that immediate imprisonment was imposed in the "vast majority of such cases", in which a maximum penalty of 20 years' jail applied.

She accepted Maqi was genuinely remorseful, had good prospects of rehabilitation and took into account his guilty plea, which had spared Mr Brewster's family and friends the ordeal of giving evidence.

But she told Maqi the community would have expected him to have exercised "extreme caution" on his first day of operating the jet ski.

Instead, he had operated the machine in a "deliberately unacceptable fashion" for about 20 minutes before the tragedy, she said.

In her victim impact statement, Mr Brewster's partner, Natalie Kurban, wrote that "no words could possibly describe the impact" of his death on her and his family.

Maqi's barrister, Ian Crisp, said his client, who has no prior or subsequent convictions, acknowledged the trauma and distress for Mr Brewster's family and friends.

His client had berated himself on the beach after the collision, punching the sand over and over, he said.

Maqi was heard to repeatedly say "stupid, stupid", before admitting that had been, "such a d---head".

The then-21-year-old had received his jet ski licence only 16 days before the fatal collision.

"This terrible experience that he caused the death of an another human being will definitely stay with him for the rest of his life," Mr Crisp said.

He added that Maqi continued to have "grave difficulties coming to terms with that".

But Mr Hevey argued the offence required "immediate imprisonment", saying "this was not simply an accident". He said Mr Bewster died "needlessly" and "as a result of the gross negligence of the accused".

Mr Hevey said the offending was not a "momentary lapse", because onlookers had warned Maqi about his conduct before the collision.

However, Mr Hevey acknowledged that Maqi was a "youthful offender", was at the "lower end of the scale of intellectual capacity" and had good prospects of rehabilitation.

Judge Davis cancelled Maqi's marine licence for five years, as she sentenced him to five years' jail. If he had pleaded not guilty and been convicted by a jury, she said, he would have been sentenced to seven years' jail with a minimum term of five years.

Maqi will serve a minimum of two years and nine months' jail, before being eligible for parole.