Local contractors say the road could be indefinitely blocked if immediate action is not taken.
The overflow saw road closures in place for much of the morning, Colac Police Chief Ken Slingsby says the issue could persist as long as the rain does.
"We're expecting that to last a fair while with the water coming over so a bit of rain's predicted over the weekend," Senior Sergeant Slingsby said.
"So it could continue for several weeks I think, so if you're driving up around the Forrest area, please take care over the next few weeks," he said.
Member for Polwarth Richard Riordan said Forrest locals are calling for urgent action following the closure of the Birregurra-Forrest Road.
He believes the flooding should come as no surprise to locals, who despite years of warning the state government, have seen no action taken.
"The mighty Barwon river is no longer flowing on it’s original course and is now flowing over the road between Yaugher road and Colac-Forrest road, shutting down critical access to Forrest, Apollo Bay and the Great Ocean Road." Mr. Riordan said.
“Vicroads must act quickly and install a new culvert to get the road open as soon as possible to assist with the return of traffic to this critical artery of our region,” he said.
“Water authorities need to immediately undertake removal of silt and weeds to restore the original course and condition of the river and prevent further road damage and flooding of farms."
“The ongoing neglect of the upper-barwon is an indictment on the state government who are dragging their feet on actioning the Upper Barwon Restoration Plan.”
“Tourism in the Otways is again threatened by State Government inaction on the environment”.