The EPA said it would not name the business responsible at this stage.
Heavy rain over the weekend flushed the pink pollutant from the creek, which had returned to normal by Monday morning.
The EPA first advised residents to avoid contact with the water on Saturday.
But Jade Borjesson saw the pink sediment leaking out of a stormwater drain near Norfolk Court on Wednesday, days before the creek turned pink.
“At that point it had not yet seriously entered the creek,” Ms Borjesson told The Age.
“It’s not clear what the EPA did between Wednesday and Saturday … We thought it would have been pumped or removed from the waterway somehow, before it reached the creek.”
She described the pollution as a fluorescent magenta pink, “it was extremely vivid and concentrated in colour”.
A spokesman from Melbourne Water said it was notified by the EPA on Thursday, and placed two lots of booms in the creek on the same day to contain the pollution.
The EPA traced the drains back to identify the source of the pollution and tested the water.
“We always encourage the public to report pollution and the local community got right behind this. We thank them for their vigilance. Officers attended on Wednesday and Saturday, worked closely with Melbourne Water and are assessing the appropriate action to take next,” Mr Settle said.
David Pavone, president of the Friends of Edgars Creek, had hoped the pollution would not turn out to be “horrendously toxic”.
“Slightly downstream from where that inflow starts, I was looking at some eels a week and a half ago,” he said.
If the pollutant was deoxygenating, that would be “death to everything”, Mr Pavone said.
“We’re sort of lucky in some ways that it coincided with the rain.”
Edgars Creek runs for 17 kilometres from Wollert before joining the Merri Creek at Coburg North and is populated with native bird species.
Melbourne woman Tara DeGraft-Hayford saw the polluted water on Saturday morning while walking her dog.
“I thought it was a plastic sheet and as I got closer, I noticed it was coming from the drain and the water was actually pink,” she said.
“It looked quite thick and so bright, almost like some kind of soap – but not. It was weird.”
Last year, Stony Creek in Yarraville ran blood-red after a five-litre bottle of dye blew over in the wind and broke.
The EPA revealed the company behind the pollution was Brooklyn-based Marchem Australasia, a chemical manufacturing company, and ordered the business to take steps to prevent any further waste leaving its premises.
You can report pollution by calling 1300 EPA VIC (1300 372 842) or emailing firstname.lastname@example.org.
Rachel is a breaking news reporter for The Age.