Fire crews are battling to contain a major chemical spill on the Great Western Highway at Katoomba in the Blue Mountains, after a truck overturned and 20,000 litres of a bright green industrial chemical poured out.
Protective bunds have been built around the spill site to stop the chemical, which is possibly a type of hydraulic fluid, reaching the iconic Leura cascades.
Westbound traffic on the Great Western Highway is being diverted, but eastbound traffic is still flowing.
The chemical is described as biodegradable, but it can be a toxic irritant to skins and eyes if touched.
Six fire crews were at the site at 5pm, plus a hazardous materials unit from St Marys, a spokesman for Fire and Rescue NSW said.
National Parks rangers, Blue Mountains council staff and fire crews are monitoring the extent of the spilled fluid, some of which entered the drainage system. Council staff have poured gravel around the edge of the spill area to try and contain it.
The truck rolled over at about 2pm, and the driver's condition is unknown, although he or she was understood to not have been trapped in the vehicle.
Ben Cubby is the Herald's environment editor