The NSW Environment Protection Authority (EPA) has identified the pollutant which caused a major crayfish kill in a tributary of Hazelbrook Creek in the Blue Mountains last month.
Initial lab testing has found the insecticide Bifenthrin in water, sediment, and crayfish samples collected from the impacted creek.
Bifenthrin is commonly used for general pest control, such as for termites, spiders, ants, and cockroaches and is highly toxic to crayfish and other aquatic organisms.
The EPA investigation into the source of the Bifenthrin pollution is being finalised.
Herbicides used by Blue Mountains City Council to control weeds, such as Glyphosate, have been ruled out as the cause of the crayfish kill and Council is not a subject of the ongoing investigation.