The Yarra River is the main river running through the city of Greater Melbourne
The river has its origins at Mount Gregory in the Great Dividing Range, Australia's only real mountain range (and a pissy one at that). It winds its way through Melbourne's suburbs and through the City into Port Phillip Bay. In its early stages, much of the river's water is used for drinking.
The river is central to the city's life. Melbourne began as a farming town with a port for recieving supplies from Tasmania, and without the river things would have been pretty tough. Discovery of gold in central Victoria led to Melbourne's rapid development and the city's port became the largest in Australia. Nowadays the port is smaller, and much of the land which it occupied is being developed as residential, commercial and park land. The river is used for rowing, kayaking, fishing and even for swimming. There are bicycle paths straddling the river banks for many kilometres. The river also features heavily in the annual Moomba carnival, used for birdman competitions, speedboat races, water+light shows and more.
Since Melbourne was founded, Melburnians have modified the river to their own ends. Early on, a waterfall which seperated the fresh and salt waters was removed to allow for the passage of boats. Other modifications have mostly to do with the prevention of flooding - Melbourne's current inner-city upper class suburbs were originally prestigious because they were located on higher ground, and hence did not suffer the annual floods. In order to prevent this the river's banks were steepened and in one case a billabong was modified in order to create an island (Herring Island).
The river is a light brown colour, like tea with a dash of milk. This has often led tourists and even ignorant Melburnians to assume that this is a sign of heavy pollution. It is true that for a long time Melbourne lacked a sewage/drainage system, and therefore the river was filthy with industrial and human waste. However with the construction of Melbourne's sewers and the Sewage Treatment Plant at Werribee, the problem was greatly alleviated. Industrial waste took longer to eradicate and of course the problem isn't at all solved (in fact it was made worse in recent years by Jeff Kennett's funding cuts to the EPA), but all in all the Yarra is a pretty clean river. There are fish in it, and people swim even in the lower (inner city) parts. The colouring is due to a combination of decomposing gum leaves and silt in the upper regions.
The river's name comes directly from the local Aboriginal group, the Wurundjeri - "yarra yarra" means "ever flowing".
The main tributaries of the Yarra River within Greater Melbourne are the Plenty River, Diamond Creek, Gardiners Creek, Moonee Ponds Creek, Merri Creek, Darebin Creek and the Maribyrnong River.