Sydney Harbour is a paradox: one of the most beautiful harbours in the world, yet few other estuaries are as modified and polluted. Many sites in the Harbour don’t meet water quality guidelines for contaminants such as nutrients and faecal bacteria. Water quality is worst in places like Silverwater Bridge, Parramatta Weir, Lane Cove Weir and Tunks Park in Middle Harbour.

Harbour sediments contain a variety of contaminants, the worst of which are dioxins, heavy metals and organochlorine pesticides (e.g. DDT). Except for a small area near the entrance, all sediments exceed guidelines for at least one contaminant. The most polluted sediments are found in Homebush Bay, Hen & Chicken Bay, Iron Cove, Rozelle Bay, Blackwattle Bay and Long Bay.

Microplastics (fragments smaller than 5mm) are an emerging problem. Early studies have found alarming levels. While the Government is working towards eliminating one source – microbeads in products like shampoo – it appears that the largest source are clothing fibres from washing machines.

Most sediment contaminants entered the Harbour prior to 1970, when industrial practices were poorly regulated. Today, three primary sources pollute the waters and sediments of the Harbour: stormwater, sewage overflows and leachate from contaminated reclaimed land.

What can be done? Current sources that can be addressed include stormwater, improved management of which can significantly reduce levels of heavy metals and other pollutants. Greater Sydney Local Land Services and local governments are undertaking key initiatives. As for pollution already in the Harbour, it appears technically and financially impractical to deal with the most contaminated sediments because of the extent of the problem.