The NSW Environment Protection Authority (EPA) is investigating the dumping of building material and debris at Collector.
On Thursday, EPA officers inspected the site on Collector Road, heading towards Gunning, which it's understood had been used as a temporary lay down area for waste by Upper Lachlan Shire Council (ULSC).
At the time, council officers were removing the waste, but would not confirm where it was to be taken.
A spokesperson from the EPA said they had "received a report of several truckloads of material from council works being stockpiled without erosion control beside a scenic road on the Lake George Escarpment".
The complainant said the building material was concrete waste from the construction of a footpath on Church Street, Collector; and the debris was from blocked drains.
ULSC acting general manager Andrew Croke said the council was assisting the EPA with the investigation and "it would be inappropriate to comment until the investigation has concluded."