Australia's second-longest river in its own right (the longest being its tributary the Darling), this 2500-odd kilometre long river drains most of inland Victoria, New South Wales, and southern Queensland. Carrying only a small fraction of the water of other, comparably-sized rivers, and with a great annual variability of its flow, in its natural state it has even beenknown to dry up completely in drought years. For most of its length, the Murray is an old, sluggishly meandering river, weaving its way across Australia's inland plains, forming the border between New South Wales and Victoria as it wanders north-easterly, before turning south-easterly for its final 500 kilometres or so into south Australia. It supplies much of Adelaide's domestic water supply.
In the 19th century the river used to support a substantial steamboat commercial trade, but the unreliable levels made it impossible for the boats to compete with the railways and later road transport. However, the river still carries a large volume of pleasure boats along its entire length. During the 20th century a large number of dams were constructed in the river's headwaters, including the Hume Dam, Dartmouth Dam, and the complex dam and pipeline system of the Snowy Mountains Scheme. These dams inverted the patterns of the river's natural flow, originally winter-spring flood and summer-autumn dry and now low through winter and full during summer; these changes ensured the availability of abundant water for irrigation, making the Murray valley Australia's most productive agricultural region, but has completely disrupted the life cycles of many ecosystems both inside and outside the river, and the irrigation has led to dryland salinity that now threatens the agricultural industries.
The disruption of the river's natural flow, runoff from agriculture, and the introduction of pest species like the European Carp has led to serious environmental damage along the river's length and has led to concerns that the river (and thus Adelaide's water and the irrigation water) will be unusably salty in the medium to long term. Efforts to alleviate the problems proceed but political infighting between various interest groups stalls progress.