A Noongar Traditional Owner has been left "absolutely shattered" after a local shire council decided against supporting the dual naming of a culturally, physically and spiritually significant river in Western Australia's south-west.

Proud Wadandi/Pibulmun, Menang Elder, Sandra Hill says she's extremely disappointed in the Shire of Boyup Brook's decision to not support the dual naming of the Blackwood River to include its Indigenous name, Goorbilyup.

Ms Hill said she first heard about the Shire's decision to deny the Blackwood River's dual naming after being contacted by the media.

"And I was shattered, I was absolutely shattered," Ms Hill said.

"We've been working on it for over a year, and we had the support of all (the other) shires.

"You can imagine the amount of work it takes to get all the cultural custodians and the Elders to agree to this."

Ms Hill said the Blackwood River runs through four other shire council areas, all of which were in support of its dual naming.

They include the Shire of Augusta Margaret River Council, Nannup Shire Council, Shire of Bridgetown-Greenbushes and Shire of West Arthur.

"The other shires just said 'this is just the right thing to do, and it'll be good for our regions in terms of tourism and in terms of reconciliation,'" Ms Hill told National Indigenous Times.

"They didn't put it out there for people to vote on it, they just said… 'It's a good thing to do. It'll benefit us.'"

The 270km-long Blackwood River is Western Australia's longest continually flowing river and a major catchment of the state's south-west.

Ms Hill said it is also of strong significance to Noongar people.

"The Goorbal is your intestine, your gut. And Bilya is 'river or waterway' and up means 'place of', so it's the place of the the intestine waterway which feeds the entire south-west nation," Ms Hill told National Indigenous Times.

"To us it's the stomach, it's the water that nourishes Noongar country.

"It's culturally significant, it's registered as a cultural Aboriginal site, the whole length of it…

"So it's culturally significant, physically significant and spiritually significant.

"It's the most significant waterway in the whole of the south-west, and that's all 14 language groups (who) recognise and understand the significance of that river."

According to Ms Hill, the Shire of Boyup Brook publicly consulted on the proposed dual naming of the Blackwood River however it is unclear at this stage whether the shire initiated consultation with any Traditional Owners in the area.

"They put it out to the community and said 'do you want this or not' and Boyup Brook is full of… colonist ancestors," Ms Hill said.

"They're all landowners out there. They all are very, very racist, I'll just be honest.

"Not all of them but most of them."

Ms Hill said she understands two thirds, six out of nine Boyup Brook Shire councillors voted against the proposal.

"And apparently there were 10 submissions put in saying 'no, we don't want it,'" she said.

Adding insult to injury, Ms Hill said no Traditional Owners were contacted by Boyup Brook Shire council ahead of the announcement, with the council notifying the public of their position via social media.

"Boyup (Brook) was the last one, but they didn't contact anyone. They just put it out there on a Facebook post," Ms Hill said.

"All we wanted was dual naming. It would still have Blackwood there, but it would also have Goorbilyup which has been its name for 65,000 years.

The Shire of Boyup Brook have not responded to questions posed by National Indigenous Times.