Contaminated waterways in Melbourne's west will take "some time" to recover after toxic runoff from a suspicious factory fire killed off wildlife including fish and birds.
The blaze at the West Footscray factory started in the early hours of August 30 with an acrid smoke plume shutting schools, businesses and run-off from the factory flowing into Stony Creek.
"At this stage we can't say how long it will take for the creek to return to normal, but we know it will take some time," Environment Protection Authority chief executive Cathy Wilkinson said on Wednesday.
Weeks after the blaze, residents are still being told by the authority to keep themselves and pets away from Stony Creek due to contamination.
People are also warned not to eat fish caught in the creek or in lower part of the Yarra River from the West Gate Bridge.
Water quality sampling is occurring weekly and while concentrations of a number of chemicals have reduced significantly, there's still a couple of readings above recreational water quality standard, Dr Wilkinson said.
Maribyrnong Council is now the lead agency in charge of the clean-up but it has been unable to determine the damage to waterways.
Friends of Stony Creek president Steve Wilson said it would take years to return the creek to normal.
"It could take years before it's back to where it was ... all the chemicals have killed off the fish, eels and even the vegetation above the creek," Mr Wilson said.
"It's a big job to restore, but if there's a proper clean up it could take between three to four years, but worst case scenario up to ten years."