A truck accident north of Melbourne earlier this week has spilt 800 litres of “non toxic” iron oxide dye into the Campbellfield Creek basin.
The Environmental Protection Authority said it had the potential to impact local plants and wildlife.
According to Melbourne Water, around 17 million litres of water had been contaminated, and most of it was still inside the wetland.
Melbourne Water was working around the clock on the spill but could not say how long the clean-up would take.
Officials said while barriers had been set up to contain the red dye, contaminated water had started to flow into Merri Creek and crews.