A five-litre bottle of dye that blew over in the wind and broke is the reason Stony Creek in Melbourne's west turned a startling shade of red at the weekend.

People had been warned earlier this week to avoid contact with the creek after a section in Yarraville ran blood red.

Steve Wilson and David Lewis, of the Friends of Stony Creek, were lamenting the condition of the wetland on Monday after it ran blood red. Credit:Chris Hopkins

On Thursday, the Environment Protection Authority revealed the company behind the pollution was Brooklyn-based Marchem Australasia, a chemical manufacturing company, and ordered it take steps to prevent any further waste leaving its premises.

Stephen Lansdell, EPA regional manager, said the business was investigating how one of its drains was connected to a rainwater pipe that feeds into a stormwater drain, despite previously conducting a plumbing survey at the site.