WESTERN Highway Alternative Mindsets is demanding an immediate stop to all work on the duplication between Ararat and Beaufort.
That is in response to revelations VicRoads bungled the estimated impact of the project on hundreds of native old growth trees.
A mistake such as this has the potential to cause massive disruption between Ararat and Stawell- Helen Lewers
VicRoads has admitted 885 large old and scattered trees will be lost during the project, far greater than 470 as estimated in the 2012 Environment Effects Statement.
WHAM spokesperson Helen Lewers said work on the Western Highway duplication should be brought to a halt.
She said the State Government needs to intervene and launch an independent review into how the severe miscalculation could have occurred.
"It should be stopped, it should have stopped at the time VicRoads first realised what it was doing," she said.
"An Environment Effects Statement is supposed to be the highest level of environmental assessment that a project can be subject to in Victoria.
"How was this overlooked? Where have the checks and balances been throughout this entire process?
"There needs to be another EES with no more spin from VicRoads."
The EES evaluated the potential impact on road endangered species such as the Golden Sun Moth and Spiny Rice Flower (a ground cover plant).
It estimated that 221 large, old trees would be impacted and a further 249 scattered trees were included in the appendices of the report.
Subsequent on the ground counting identified an impact to 1635 large old and scattered trees.
VicRoads executive director Mick McCarthy said engineers and stakeholders have been working to reduce the impact.
"We are working with everyone involved to understand how the discrepancy occurred," he said."We have begun contacting affected landowners and stakeholders to explain that it does not mean the project is on hold."
VicRoads now expects to impact 885 large old and scattered trees from Beaufort to Ararat.
To date, about 620 of the trees have been removed between Beaufort and Buangor.
Ms Lewers said the destruction of the trees was nothing short of an 'environmental catastrophe'.
"This signifies the loss of so many incredible beautiful old red gums that we're irreplaceable," she said.
With planning now underway for the duplication from Ararat to Stawell, Ms Lewers said the mistake sets a concerning precedent.
"A mistake such as this has the potential to cause massive disruption between Ararat and Stawell," she said.