The preferred alignment of the proposed F6 Extension goes through the Rockdale Wetlands and the Royal National Park a site with some of the "richest concentrations of plant species in temperate Australia".

The assessment, in a leaked Roads and Maritime Services report, also confirms that about 14 hectares of bushland, trees and wetlands will be cleared between Arncliffe and Loftus.

The first section of the $14.5 billion toll road, between WestConnex at Arncliffe and President Avenue, Brighton-Le-Sands, would be built primarily on land historically reserved for the freeway.

The "corridor of connecting natural and open space" forms part of the Rockdale Wetlands and Recreation Corridor.