Toby Jamieson, who worked as a groundskeeper at Canberra Grammar School, disappeared beneath the waters of the Murrumbidgee River on Thursday afternoon.

His family told The Canberra Times how more than 20 complete strangers banded together to try to save the 35-year-old, taking turns to search the murky river, before he was eventually found just before dark.

His sister Amy said he had swum in those waters all his life.

"It was our favourite spot," she said. "He was swimming in there since he was a baby. He was fit and healthy. We still don't understand what happened."

Police said his death was a tragedy and they did not consider it to be suspicious. A report will be prepared for the coroner.

Wife Linda described how four women rushed out to swim her children to safety when they heard her calling for help.

"I could see he was struggling and they came straight away to help, the bystanders [and emergency services] were just beautiful, they searched for him for so long, they looked after the kids and kept them distracted.

"Even after I was exhausted, they searched and searched."

A true green thumb, Mr Jamieson had been preparing for a trip abroad to England to work on the grounds of Headingley Oval ahead of the upcoming Ashes test.

"He was always outside, he didn't sit down," Linda said.

"He was very patient and very cuddly, he had a certain cheekiness. He loved his kids [William and Sophie] very much, he was born to be a father I think."

The family now hopes to thank those who came to their aid personally.

"We will be forever grateful to the brave people who pushed themselves to the limit to try and save him," they said in a statement.

"We would love to ... make contact with anyone who assisted on the day."

"We are finding peace in the fact that Toby died in a place that holds so many beautiful memories for our family."

Amy said her brother was humble, quiet and at his happiest with family.

"He would have hated all this attention," she said.

He was also a rugby league tragic, complete with his own Raiders jerseys and number plates, having followed the club since he was a boy.

"He never missed a home game," Linda said.

"And he always had such a beautiful garden, he was the first to help anyone with landscaping or giving plant advice. He was always helping people. I don't know where he got the energy.

"He just brought joy."

Head of school at Canberra Grammar Justin Garrick also spoke of Mr Jamieson's "quiet nature" in a letter to parents on Tuesday.

"Our school is a community in times of grief as well as happiness," Dr Garrick wrote.

"All who admire and enjoy the beauty of our school grounds will know that they are a tribute to Toby and his closest colleagues in the grounds and maintenance department, who are feeling his loss most keenly."

At Mr Jamieson's funeral, to be held at the Canberra Grammar chapel at 10.30am on Saturday, the young father will also be remembered by his parents Andrew and Rhonda, niece Aurora and nephew Thomas.

In lieu of flowers, people are urged to donate to Charity Water, which delivers safe drinking water to developing countries.

"One hundred per cent of donations go to clean water (that's why Toby really liked them)," the family said.

ACT Policing advised the community to take care over summer, whether swimming in waterways, or public or private pools.

In the next three years, Royal Lifesaving ACT is hoping to run a pilot program that would see lifesavers watching over inland swimming holes, including Casuarina Sands.