The deaths of about 1,000 giant spiny crayfish are being investigated by the Environment Protection Authority in a likely pollution incident in the Blue Mountains this week.
Hundreds of dead crayfish were found in a tributary of Hazelbrook Creek, near Horseshoe Falls, on Wednesday by a tour guide.
Blue Mountains city council staff sent to investigate the reports discovered up to 1,000 dead or dying crayfish across an area of at least 600 metres downstream from the Oaklands Road and Hall Parade intersection in the mountain town of Hazelbrook.
The creek drains a subcatchment adjacent to a mostly residential area of the town.
The EPA is leading the investigation to identify the pollutant along with officers from Blue Mountains city council.
Crayfish carcasses have been taken to an EPA laboratory in Lidcombe where they are being tested with a view to identifying the toxicant and isolating the source.
Blue Mountains mayor Mark Greenhill said in a statement on Thursday that the council would continue working closely with the EPA on the matter.
The council advised both humans and their pets to avoid contact with the water in the creek or the affected crayfish until the investigation had determined a cause of death for the crayfish.
On Friday, the council said the investigation had narrowed the possible pollution source to a small area within the Horseshoe Falls catchment.
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A council spokesperson told Guardian Australia it was not aware that any other wildlife in the area had been significantly affected, but stressed the matter was still under investigation.
Giant spiny crayfish are native to Australia and are very vulnerable to pesticides, runoff and habitat destruction. It is illegal to trap them in Blue Mountains swamps or waterways.
It’s not the first time they have been hit by a pollution event in the area. In 2012, bifenthrin – a toxicant used for termite control – contaminated Jamison Creek in the World Heritage Wentworth Falls area, resulting in a similarly sized mass crayfish kill, the largest ever at the time.
The toxicant, which entered the creek via stormwater drains, also caused the death of other macroinvertebrates in the waterway, and resulted in a massive reduction of aquatic biodiversity, taking the taxonomic families in the creek from 22 down to just three.
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