The dumped substance that turned a Wollongong creek bright green last week closely resembled another spill in a city waterway earlier this year.
But Wollongong City Council said testing showed Span 85, the industrial surfactant from the earlier spill, was not last week's fluorescent intruder.
Emergency services were called to Musgrave Place in Figtree about 11am on Thursday, October 19, after a creek running near homes and a childcare centre turned bright green.
Five fire trucks, a specialist HAZMAT crew, council staff and the Environment Protection Agency (EPA) were called in to the 'Kermit the frog' coloured waterway, which runs into American Creek and to Port Kembla Harbour.
The green substance was traced upstream through the drainage system to a drain in a soccer field off Richards Street in Unanderra.
In April a resident noticed pollution had turned a creek under Gipps St in Wollongong a similar shade of bright green in late April, and alerted councillor Cath Blakey, who raised the alarm.
The council, which has called for public help identifying the recent culprit, said the chemicals were not the same.
The Gipps St pollutant was quickly identified by the council as a substance called Span 85, which is a biodegradable surfactant used in many industrial applications.
The council said it had not found the culprit from the April incident.
"Wollongong City Council was unable to identify the source of a previous pollution incident (April 2023) in a creek under Gipps St in Wollongong," a spokeswoman said.
"Fire and Rescue HAZMAT officers attended both pollution events and tested water samples using their mobile laboratory.
"The creek water in Figtree, did not contain the same chemicals as identified earlier in the year at Gipps St."
While the Gipps St location had several light industrial operations backing onto the creek nearby, raising the possibility of an accidental spill.
But the Figtree dumping was almost certainly done deliberately, by someone who took the substance to the soccer field, opened the grate, and dumped it into the creek.
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