Rebecca and Peter Yeoman's daughter Milly became a quadriplegic at 12 years of age after she was instructed to dive into shallow water during a school swimming lesson at the Swim and Survival Academy in November 2016.

A centre employee instructed Milly to dive into the pool, which was about 1.2 metres deep. She hit her head on the bottom of the pool, causing the spinal injuries.

Milly was 23 centimetres taller and heavier than the average female her age but was still told to dive into the shallow water.

The husband and wife owners of De Kort Enterprises, trading as Swim and Survival Academy, appeared in the County Court in Ballarat on Thursday for sentencing.

They were convicted and fined $150,000, an amount the victim's family said was not enough. The maximum penalty for breaching the Occupational Health and Safety Act is $1.4 million.

Milly's parents Rebecca and Peter Yeoman appeared upset when they left the court room straight after the sentence was announced.

Outside the court building, Mrs Yeoman told reporters the fine was not near enough to the $1 million fine they were hoping for.

In sentencing, Judge Paul Lacava said "this was a serious example of a serious offence".

He said the company should have known the risks of diving into shallow water, which a grade six pupil would not have understood.

The judge said the diving lesson could have been moved to another part of the swimming pool at no cost to the swim company.

He said the accident had had an impact on every aspect of the victim and her family's everyday lives.

"Members of her family have been turned upside down because of this tragedy," Judge Lacava said.

The judge said he took into account the swim centre owner's early guilty plea and their financial situation.

He said the owners were truly sorry for the accident and they had taken steps to ensure it would not happen again.

They pleaded guilty in November to breaching the Occupational Health and Safety Act for failing to ensure the centre was safe.

Judge Lacava said he would have imposed a $250,000 fine with conviction if the owners did not plead guilty.

Have you signed up to The Courier's variety of news emails? You can register below and make sure you are up to date with everything that's happening in Ballarat.