The Hawkesbury-Nepean River catchment is one of the largest coastal basins in NSW with an area of 21,400 square kilometres. The catchment at Penrith is 52% of the total area and of this portion, 80% is under the control of Warragamba Dam. The Nepean valley within the Penrith LGA is characterised by a relatively narrow floodplain that is divided into three parts by the river channel. The northern floodplain area encompasses Penrith Lakes and the eastern side of the valley. The channel divides the valley south of this with the western side over Emu Plains and the eastern side over the Mulgoa and Central Business District (CBD) area.