The Maribyrnong River is the second biggest river (after the Yarra River) in the Melbourne metropolitan area and runs for 160 kilometres from its source on the Great Dividing Range. It flows through an urban environment in the north western suburbs of Melbourne before connecting with the Yarra River about 3.5km upstream of the Yarra River entrance to Port Phillip Bay. The tidal influence extends about 16km upstream to what was originally a natural rock ford at Avondale Heights. This separates the upper freshwater parts of the river from the estuary.
The River and creeks in the catchment tend to be deeply incised, exhibit a highly variable flow and are subject to extended periods of low flow. They are also characterised by poor water quality and loss of riverbank and aquatic habitat. The incised valleys through which they flow have valuable areas of remnant vegetation, including the highly valued river red gum.
The local community have highlighted the most important environmental values of the waterways, which include the remaining native vegetation, platypus and growling grass frogs. The Lower Maribyrnong is particularly valued for recreational opportunities including boating, kayaking, fishing, rowing and bike riding. Unfortunately, the waterway and the bay into which it flows remains threatened by several key pollutants and challenges such as urban growth and climate change.