Murray River

The Murray forms part of the 3,750 km (2,330 mi) long combined Murray-Darling river system that drains most of the inland of Victoria, New South Wales and the southern part of Queensland. The Murray carries only a small fraction of the water of comparably sized rivers in other parts of the world, and with great annual variability of its flow. It has dried up completely during extreme droughts on three occasions since official record-keeping began. More often, a sandbar formed at the mouth and stopped the flow.

The Murray is the border between New South Wales and Victoria, specifically at the top of the left bank (i.e. the Victorian side of the river). In a 1980 judgement, the High Court of Australia ruled on the question as to which state had jurisdiction in the unlawful death of a man who was fishing by the river's edge on the Victorian side of the river. This boundary definition can be ambiguous, since the river changes its course over time, and some of the river banks have been modified.

For 11 km (6.8 mi) west of the line of longitude 141°E, the border is between Victoria and South Australia, in the middle of the river. The discrepancy was caused during the 1840s, when the border was originally surveyed, by an east-west miscalculation of 3.72 kilometres (2.31 miles), and led to a long-running boundary dispute. West of this sector, the Murray is entirely within the state of South Australia.

Centred on the river is the Murray agricultural region, which consists of nine local government areas:

• Albury
• Balranald Shire
• Berrigan Shire
• Edward River Council
• Federation Council
• Greater Hume Shire
• Murray River Council
• Wentworth Shire
• Snowy Valleys Council

Major settlements

Major settlements along the course of the river, from its source to the Southern Ocean, and their populations from the 2016 Australian census are as follows.

The Murray and its tributaries support a variety of river life adapted to its vagaries. This includes native fish such as the famous Murray cod, trout cod, golden perch, Macquarie perch, silver perch, eel-tailed catfish, Australian smelt and western carp gudgeon, as well as other aquatic species such as the Murray short-necked turtle, broad-clawed yabbies and the large-clawed Macrobrachium shrimp 67, in addition to aquatic species more widely distributed through Southeastern Australia such as common long-necked turtles, common yabbies, the small claw-less paratya shrimp, water rats and platypus. The Murray crayfish, an endangered species, was able to increase its numbers thanks to scientists. The Murray also supports fringeing corridors and forests of the river red gum.

The health of the Murray has declined significantly since European settlement, particularly through regulation of its flows. Extreme droughts between 2000 and 2007 put significant stress on river red gum forests, leading to mounting concern over their long-term survival. The Murray has also flooded on occasion. The most significant was the flood of 1956: lasting for up to six months, it inundated many towns on its lower reaches in South Australia.

Lake Bungunnia

Between 2.5 and 0.5 million years ago, the Murray terminated in a vast freshwater lake, Lake Bungunnia, formed by earth movements that blocked the river near Swan Reach. At its maximum extent, Lake Bungunnia covered 33,000 km² (12,741 sq mi), extending to near the Menindee Lakes in the north and to near Boundary Bend in the south. The draining of Lake Bungunnia occurred approximately 600,000 years ago.

Deep clays deposited by the lake are evident in cliffs around Chowilla in South Australia. Considerably higher rainfall would have been required to keep such a lake full; the draining of Lake Bungunnia appears to have marked the end of a wet phase in the history of the Murray-Darling Basin and the onset of widespread arid conditions similar to today. A species of Neoceratodus lungfish existed in Lake Bungunnia; today Neoceratodus lungfish are only found in several Queensland rivers.

Cadell Fault and formation of the Barmah red gum forests

The noted Barmah River red gum forests owe their existence to the Cadell Fault. About 25,000 years ago, displacement occurred along this fault, raising its eastern edge, which runs north-south, 8 to 12 m (26 to 39 ft) above the floodplain. This created a complex series of events. A section of the original Murray River channel immediately behind the fault was rendered abandoned (it exists today as an empty channel known as Green Gully). The Goulburn River was dammed by the southern end of the fault to create a natural lake.