The Swan River estuary flows through the city of Perth Western Australia. Its lower reaches are relatively wide and deep, with few constrictions, while the upper reaches are usually quite narrow and shallow.
The Swan River drains the Avon and coastal plain catchments, It has three major tributaries, the Avon River, Canning River and Helena River. The latter two have dams (Canning Dam and Mundaring Weir) which provide a sizeable part of the potable water requirements for Perth and the regions surrounding. The Avon River contributes the majority of the freshwater flow. The climate of the catchment is Mediterranean, with mild wet winters, hot dry summers, and the associated highly seasonal rainfall and flow regime.
The Avon rises near Yealering, 100 kilometres (62 mi) southeast of Perth: it meanders north-northwest to Toodyay about 90 kilometres (56 mi) northeast of Perth, then turns southwest in Walyunga National Park – at the confluence of the Wooroloo Brook, it becomes the Swan River.
The Canning River rises not far from North Bannister, 100 kilometres (62 mi) southeast of Perth and joins the Swan at Applecross, opening into Melville Water. The river then narrows into Blackwall Reach, a narrow and deep stretch leading the river through Fremantle Harbour to the sea.