The Environmental Protection Authority is investigating the spill, which caused a hydrocarbon, oil-based substance to pollute Stony Creek, behind Rutherford Industrial Estate, on Thursday.

EPA Hunter Region manager Adam Gilligan said investigations were ongoing.

“Our officers have been taking more samples for analysis whilst supervising the clean-up that took place over the weekend,” he said.

“Results from recent testing will be available over the course of the coming week.”

EPA officers have taken samples from the creek as well as from nearby businesses.

They are looking for a match to identify which business the hydrocarbon came from.

The pollutant is believed to have entered the creek through a stormwater drain.

Fire and Rescue NSW hazardous material crews from Maitland and Newcastle removed the material from the surface of the water.

Lower Hunter zone commander Superintendent Greg Windeatt told the Mercury last week |that, while there were traces of the toxic substance in the air, the levels were not high enough to be a danger to people.

Anyone who has information about the spill is asked to phone the EPA environment line on 131 555.