"It's not an isolated incident," he said. "It's just that this is by far the biggest and most spectacular.” He said the string of pollution events had led his environmental consultancy – which specialises in water pollution – to try and work out who was behind the "woeful act" of environmental vandalism. While he said Bio2Lab was yet to begin an investigation – which was being funded by a charity group – he believed it was most likely a business, or several businesses, were deliberately pouring chemicals down the drain to cut costs.

Dandenong Creek on Sunday. Credit:First Friends of Dandenong Creek Dr Sharley said the chemical was a surfactant and would have been used as a cleaning agent on an industrial scale. Reader Coady took this photos of his kids walking alongside a very foamy Dandenong Creek. "I’m just flabbergasted as to volume that must have been put into system," Mr Sharley said. "We're talking, I reckon, drums – 44-gallon drums – that type of volume.

A reader took this photo of Dandenoon Creek at Waterford Valley Golf course in Rowville. "We're not talking about someone who's dropped a bottle of detergent down the sink by accident." University of Melbourne's Centre for Aquatic Pollution Identification and Management (CAPIM) chief executive officer for Vincent Pettigrove agreed on the likely source but disagreed on the motivation. "A lot of the time, although people tend to think its material that is being poured straight into the drains, often times it can just be poorly stored on premises, it could be a leaky drum," he said. "In this case, we don't know, it's still a mystery."

Due to the profile given earlier foaming events he said this was unlikely to be a deliberate act. But the associate professor said he was very confident the culprit or culprits would soon be identified. Professor Pettigrove said CAPIM had been working with Melbourne Water, the Environmental Protection Agency and the City of Greater Dandenong for several years to tackle pollution in the catchment. "It's disappointing this has happened, now we're going to have to work very hard in the next few weeks to locate the source," he said. He said there were already clues, with the foam events appearing to occur on weekends.

Dr Sharley agreed those responsible could be tracked down by man-hole sampling and analysis of chemicals. If that were to occur, he said if his suspicions of deliberate dumping proved true, regulators must name and shame the culprits. "I've been working in this area for eight to nine years, looking at storm-water pollution and it is very frustrating, it seems to be an endless battle," he said. "But we are making headway, and this is the opportunity to really make a public announcement that this type of blatant polluting of the environment cannot keep going on. "I hope that someone is made accountable for this – and in a big way."

Earlier EPA executive director of regional services Damian Wells warned any rogue operators found responsible for the spill could face anything from a $8000 fine to prosecution in the courts, and urged anyone with information on the source of the pollution to contact the environmental authority's hotline on 1300 EPA VIC.