The Murrumbidgee River is a major river in the state of New South Wales, Australia, and the Australian Capital Territory (ACT). A major tributary of the Murray River, the Murrumbidgee travels from the Fiery Range of the Snowy Mountains, through the ACT, and to a confluence with the Murray.
The mainstream of the river system flows for . The river's source in the Fiery Range of the Snowy Mountains, part of the Australian Alps near Mount Kosciuszko and it flows to a confluence with the Murray River. For , the river flows through the Australian Capital Territory near Canberra, picking up the important tributaries of the Molonglo and Cotter Rivers. The Murrumbidgee drains much of southern New South Wales and all of the Australian Capital Territory, and is an important source of irrigation water for the Riverina farming area.
The river system's current channels are relatively new with the Upper Murrumbidgee being an anabranch of the Tumut River (that once continued north along Mutta Mutta Creek) when geological uplift near Adaminaby diverted its flow. The contemporary Murrumbidgee starts at Gundagai but generally the stream that now includes the Upper Murrumbidgee is described as being part of the full river.
In June 2008 the Murray-Darling Basin Commission released a report on the condition of the Murray-Darling basin, with the Goulburn and Murrumbidgee Rivers rated in a very poor condition in the Murray-Darling basin with fish stocks in both rivers were also rated as extremely poor, with 13 of the 22 native fish species found in the Murrumbidgee River.
The Murrumbidgee River was known to Europeans before it was actually discovered by them. In 1820 the explorer Charles Throsby informed the Governor of New South Wales that he anticipated finding "a considerable river of salt water (except at very wet seasons), called by the natives Mur-rum-big-gee". In the expedition journal, Throsby wrote as a marginal note: "This river or stream is called by the natives Yeal-am-bid-gie ...". The river he had stumbled upon was in fact the Molonglo River, Throsby reached the actual river in April 1821.
In 1823, Brigade-Major John Ovens and Captain Mark Currie reached the upper Murrumbidgee when exploring south of Lake George. In 1829, Charles Sturt and his party rowed and sailed down the length of the river from Narrandera to the Murray, and then down the Murray to the sea. They also rowed, sailing when possible, back up against the current. The Murrumbidgee basin was opened to settlement in the 1830s and soon became an important farming area.
Here we may remark on the tenacity with which the Murrumbidgee River long eluded the eye of the white man. It is scarcely probable that Meehan and Hume, who on this occasion were within comparatively easy reach of the head waters, could have seen a new inland river at that time without mentioning the fact, but there is no record traceable anywhere as to the date of its discovery, or the name of its finder. When in 1823 Captain Currie and Major Ovens were led along its bank on to the beautiful Maneroo country by Joseph Wild, the stream was then familiar to the early settlers and called the Morumbidgee. Even in 1821, when Hume found the Yass Plains, almost on its bank, he makes no special mention of the river. From all this we may deduce the extremely probable fact that the position of the river was shown to some stockrider by a native, who also confided the aboriginal name, and so it gradually worked the knowledge of its identity into general belief. This theory is the more feasible as the river has retained its native name. If a white man of any known position had made the discovery, it would at once have received the name of some person holding official sway.
The river has risen above at Gundagai eight times between 1852 and 2002, an average of just under once every eleven years. Since 1925, flooding has been minor with the exception of floods in 1974. In the 1852 disaster, the river rose to just over . The following year the river again rose to just over . The construction of Burrinjuck Dam from 1907 has significantly reduced flooding but, despite the dam, there were major floods in 1925 and 1974.
The most notable flood was in 1852 when the town of Gundagai was swept away and 89 people, a third of the town's population was killed. The town was rebuilt on higher ground.
In 1925, four people died and the flooding lasted for eight days.
The reduction in floods has consequences for wildlife, birds and trees. There has been a decline in bird populations and black box flood plain eucalypt forest trees are starting to lose their crowns.