A number of campers said they witnessed a boat driving erratically shortly before a crash between two boats on Friday night. 

The collision left 12-year-old Courtney Keast in intensive care with serious head and facial injuries.

Courtney had two neurosurgeries at the weekend and remains in a serious condition in the Royal Children’s Hospital.

Her family said in a statement it was an extremely difficult time but they were grateful for the work of paramedics and hospital staff in caring for her.

A man in his 40s and a 15-year-old boy, who were on the same boat as Courtney, were both treated with bumps to the head and taken to Bendigo Health.

Police seized a boat on Saturday that was believed to have been involved in the collision. 

A 45-year-old Doreen man was arrested and interviewed. He has been released pending further enquiries. A police spokeswoman said the investigation remains ongoing.

A number of campers said at the weekend they avoided going into the lake during peak time because it was too dangerous when there were too many boats.

Heidi and Paul Nankervis said they have been going to Lake Eppalock for 20 years but generally avoided going in during the day.

Mrs Nankervis said she saw a boat swerving at high speed moments before the crash.

"We weren't all that surprised there was a crash that night... It was extremely busy on the water."

Mrs Nankervis said it was "the unfortunate mentality of some people who drive too fast". "Their boats are just a licence to hoon," she said.

Anthony Rogers, who takes his boat from Bendigo to Lake Eppalock during summer, said he was concerned there was a minority of people who didn't obey the laws.

But he said the penalties were severe enough for people to take caution.

"I think most people do the right thing," he said.