There would be significant and obvious damage of World Heritage wilderness and national parks upstream of the dam. The lower reaches of protected wild rivers, including the Kowmung, Coxs and Nattai Rivers, would be damaged. Flood inundation will scar wilderness areas by killing river bank vegetation and depositing sediment.
The false sense of security created by raising the dam wall will encourage the further release of low lying land on which development is currently prohibited. As many as 100,000 houses could be constructed with the following detrimental effects:
- Up to a million additional vehicle movements per day in the Hawkesbury-Nepean valley, causing traffic congestion, air pollution and resulting health problems in the whole of western Sydney;
- A huge increase in run-off and sewage discharge that will cause even worse deterioration of water quality in the Hawkesbury-Nepean River;
- Loss of rich agricultural land to urban expansion and destruction of fisheries, including the major oyster farming industry.