Victoria's environmental watchdog is investigating a discharge that has turned Stony Creek in Melbourne's west bright red, a year after a chemical fire contaminated the water.

Key points: Authorities said the pollution likely flowed into the creek through the stormwater system

Authorities said the pollution likely flowed into the creek through the stormwater system The community was advised to avoid contact with the water in the creek

The community was advised to avoid contact with the water in the creek The Environment Protection Authority said it was likely the pollution contained red dye

Environment Protection Authority Victoria (EPA) said it had received multiple reports about a "red-coloured discharge" in the creek near St Leonards Avenue in Yarraville.

"The discolouration is not naturally occurring and has likely entered the creek through the stormwater system, either as a flowing substance or as a result of run-off from the rain on Saturday," an EPA spokesperson said in a statement.

EPA investigators attended the site on Saturday and Sunday.

EPA manager Stephen Lansdell said the run-off was likely to contain red dye, but the authority was still working to confirm that was the case.

It comes just over a year after a range of chemicals were detected in the creek, including the controversial firefighting foam PFAS, following a massive fire nearby.

The industrial blaze at a warehouse in West Footscray in August 2018 burned for days, spewing toxic black smoke over the surrounding suburbs.

Firefighting foam and chemicals from the building washed into the waterway of Stony Creek at the time, with residents saying thousands of fish were killed.

The fire billowed smoke over Melbourne's west for days. ( Supplied: Kate Arnott )

It was not clear whether the latest discharge was related to the fire.

Mr Lansdell said officers had taken samples from the creek and would test the water against substances from a site they believed could be the source of the discharge.

"If the match is confirmed, EPA will not hesitate to take action in line with the Compliance and Enforcement policy," Mr Lansdell said.

"Clean-up works are expected later today."

Creek's 'technicolour history' of contamination

Friends of Stony Creek president and Yarraville resident Steve Wilson said the creek had a long history of pollution.

"It's known for its technicolour history as they say," he said.

"I've seen it blue. People have seen it a yellow colour. A cream colour.

Locals said the ecosystem of the creek was killed off following last year's fire. ( ABC News, file photo )

"White is a very prominent one that's usually from a break in the sewer line or something like that."

He said life was just starting to come back to Stony Creek after the last year's fire, and he was worried the new contamination could hinder its recovery.

"I'm a bit concerned it'll have an effect on the fish down there and slow down their recovery," he said.

"This has been ongoing ever since I've been down there. There's always been these spills down there."

Earlier this month, Melbourne Water released the Stony Creek Rehabilitation Plan, which was developed with the EPA and Maribyrnong City Council.

Mr Lansdell thanked the community members who reported the red colour, saying the reports had been "vital" in tracking the source.

To report pollution to EPA's 24-hour hotline call 1300 EPA VIC (1300 372 842).