Insecticide to blame for hundreds of dead crayfish in Blue Mountains creek last month, EPA says

An insecticide was the cause of a major crayfish kill in the Blue Mountains last month, the New South Wales environmental regulator has confirmed.

About 1,000 dead and dying giant spiny crayfish were found in a tributary of Hazelbrook Creek, near Horseshoe Falls, by a tour guide.

The creek drains a subcatchment adjacent to a mostly residential area of the town of Hazelbrook and the Environment Protection Authority said at the time the cause of the deaths was likely a pollution incident.

The regulator said on Friday that initial lab testing had found the insecticide bifenthrin in water, sediment and crayfish samples collected from the affected 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 regulator said herbicides used by Blue Mountains city council to control weeds, such as glyphosate, had been ruled out as the cause of the crayfish kill and the council was not a subject of an ongoing investigation into the source of the pollution.

Brad Smith, the acting chief executive of the Nature Conservation Council of New South Wales, said the incident was “a reminder about how careful businesses and residents need to be with chemicals, especially around waterways”.

“Especially in the Blue Mountains, we all have a responsibility to take care and look after our precious world heritage,” he said.

“We look forward to the EPA finding the source of this tragic spill.”

It is not the first time bifenthrin has been identified as the cause of a major crayfish kill in the Blue Mountains region.

In 2012, bifenthrin contaminated Jamison Creek in the world heritage Wentworth Falls area, resulting in a similarly sized mass crayfish kill, the largest ever at the time.