Jason Brailey and his family were fishing at Tanti Creek near Mornington in Victoria in late 2019 when he noticed something on the bank opposite.
Speaking with NITV News, Mr Brailey said he recognised what it was immediately and knew it was a significant find.
"It was like a cheesy movie, it was like it was glowing," he told NITV News.
After crossing the creek, Mr Brailey picked up the boomerang, looked at it, and saw that it was pre-colonial.
Later, he showed the artefact to Boon Wurrung Elder, Aunty Carolyn Briggs and eventually took it up to the Australian National University in Canberra, where archaeologist Dave Johnston began the process of dating it.
The professor came back to Mr Brailey and Aunty Carolyn with the age of the boomerang in late 2020.
"I was gobsmacked when I found out how old it was," said Mr Brailey
"I thought maybe it was a couple hundred years old - but it's 800-years-old."
The boomerang will sit with others being researched by Prof Johnston at ANU before being repatriated to Country.
"There's always a reason things happen," Mr Braily told NITV News.
"The way it was sitting on the bank, with the next big rain it could have been washed away."