The mix of diesel and what's believed to be paint thinners spilled out of a stormwater drain near Lamrock Avenue at around 5.15pm on Wednesday, with Fire and Rescue NSW called to place containment barriers across the creek.

Council staff contained the spill by Thursday, with about 100 metres or so of the creek affected.

No spill escaped downstream, according to council.

Orange City Council communications officer Allan Reeder said council was trying to determine the source of the spill.

"Council staff are looking into the network of pipes upstream from the area towards the Barrett's Estate and Kenna Street area to see if the source of how the diesel got into the stormwater system can be found," he said.

"Council investigations so far suggest the pollutant might have been diesel or perhaps a mix of paint thinners as well.

"There are indications the pollutant flowed into the creek from a nearby stormwater pipe."

Containment booms were put in place, while a waste disposal company will be on the scene on Friday to remove any contaminated materiel.

MAP: The location of Blackmans Swamp Creek

"Anyone disposing of waste diesel is reminded to contact a special liquid trade waste firm," Mr Reeder said.

"People risk an $8,000 fine if successfully prosecuted for dumping fuel into the city's sewer or stormwater systems."

Earlier on Thursday, NSW Fire and Rescue said brigades were called onto the scene on Wednesday night.

"Upon arrival a substance, believed to be diesel, was observed in the creek/stormwater canal," Leading Station Officer Dane Philippe said.

"FRNSW crews worked hard to place 12 booms in the water in order to stop the flow and prevent it from spilling further down the creek.

"I'd estimate that there was a couple of hundred litres of diesel."

The affected area ran alongside National Avenue between Sampson and Clinton streets.

Leading Station Officer Philippe said it took three hours to contain the spill and then the incident was handed over to Orange City Council.

"All three appliances from 412 Orange attended and assistance was requested from Orange City Council and the Hazmat from 216 Bathurst," he said.

Anyone with information is urged to contact Orange City Council.