Peter White is tackling the entire length of the mighty Murrumbidgee River in support of Wounded Heroes.

"I was in the Defence Force myself for 14 years, and came out with PTSD and some mental health issues," he said. "When I came across Wounded Heroes ... I knew that there was something I needed to do."

It's not the first time he has taken on a mammoth challenge, Mr White said to his understanding he was the first man to trek the Lachlan River in 2018 since explorer John Oxley.

Mr White is kayaking for four days on, and three days off to stick to his work commitments.

"I work for community corrections with the youth that go through court, so I do not want to let them down," he said. "We started up in Gundagai, up near Yass, and it has taken me six days to get here.

"On Thursday, I will start heading towards Narrandera."

Mr White said he has a support crew person who aims to meet him on the banks but has no set plans for the journey. He added he takes each challenge and each day as it comes.

"An average paddle is 35 to 50 kilometres for the day," he said. "I don't listen to music or anything, and it is just me with my thoughts. You have the water, and nature and I find it relaxing."

READ MORE: Peter White's epic Lachlan River trek for youth

A proud Wiradjuri man, Mr White, is also carrying a message stick with him along his journey.

"The way I explain it is an Aboriginal passport," he said. "The elders commission it, and in the old days, if I got caught in someone else's area, I would get a free pass with the message stick."

The Australian Horizons Foundation is supporting Mr White in his endeavour, said spokesman Mark Rudd.

"Australian Horizons Foundation is proud to be supporting Peter in this amazing kayak trek to raise funds and awareness for Defence Force personnel in need," he said.

"It is only fair we give back to those people who have sacrificed so much in their service for Australia".