Small-scale pumping plants began drawing water from the Murray in the 1850s and the first high-volume plant was constructed at Mildura in 1887. The introduction of pumping stations along the river promoted an expansion of farming and led ultimately to the development of
irrigation areas (including the
Murrumbidgee Irrigation Area). In 1915, the three Murray states – New South Wales, Victoria, and South Australia – signed the River Murray Agreement which proposed the construction of storage reservoirs in the river's headwaters as well as at
Lake Victoria near the South Australian border. Along the intervening stretch of the river a series of
locks and
weirs were built. These were originally proposed to support navigation even in times of low water, but riverborne transport was already declining due to improved highway and railway systems. The disruption of the river's natural flow, run-off from agriculture, and the introduction of pest species such as the
European carp has led to serious environmental damage along the river's length. There are widespread concerns that the river will be unusably salty in the medium to long term – a serious problem given that the Murray supplies 40 per cent of the water supply for
Adelaide. Efforts to alleviate the problems have proceeded but disagreement between various groups has hampered progress. Introduced fish species such as
carp,
gambusia,
weather loach,
redfin perch,
brown trout, and
rainbow trout have also had serious negative effects on native fish. The most pernicious are carp, which have contributed to environmental degradation of the Murray and its tributaries by destroying aquatic plants and permanently raising
turbidity. Carp is the most common species, and can be found in all segments of the river.
Reservoirs Four large reservoirs were built along the Murray. In addition to Lake Victoria (completed late 1920s), these are
Lake Hume near
Albury-Wodonga (completed 1936),
Lake Mulwala at
Yarrawonga (completed 1939), and
Lake Dartmouth, which is actually on the
Mitta Mitta River upstream of Lake Hume (completed 1979). The Murray also receives water from the complex dam and pipeline system of the
Snowy Mountains Scheme. An additional reservoir was proposed in the 1960s at
Chowilla Dam, which was to have been built in South Australia and would have flooded land mostly in Victoria and New South Wales. It was cancelled in favour of building Dartmouth Dam due to costs and concerns relating to increased salinity.
Barrages viewed from the freshwater side From 1935 to 1940 a series of
barrages was built near the Murray Mouth to stop seawater entering the lower part of the river during low flow periods. They are the Goolwa Barrage, with a length of ; Mundoo Channel Barragel ; Boundary Creek Barragel ; Ewe Island Barrage, ; and Tauwitchere Barrage, . s on the lower Murray near
Berri, South Australia These dams inverted the patterns of the river's natural flow from the original winter-spring flood and summer-autumn dry to the present low level through winter and higher during summer. These changes ensured the availability of water for irrigation and made the Murray Valley Australia's most productive agricultural region, but have seriously 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. In 2006, the
Government of South Australia released a plan to investigate the construction of controversial
Wellington Weir.
Locks Lock 1 was completed near
Blanchetown in 1922.
Torrumbarry weir downstream of
Echuca began operating in December 1923. Of the several locks that were proposed, only thirteen were completed; Locks 1 to 11 on the stretch downstream of
Mildura, Lock 15 at
Euston and Lock 26 at
Torrumbarry. Construction of the remaining weirs purely for navigation purposes was abandoned in 1934. The last lock to be completed was Lock 15, in 1937. Lock 11, just downstream of Mildura, creates a long lock pool that aided irrigation pumping from Mildura and
Red Cliffs. Each lock has a navigable passage next to it through the weir, which is opened during periods of high river flow, when there is too much water for the lock. The weirs can be completely removed, and the locks completely covered by water during flood conditions. Lock 11 is unique in that the lock was built inside a bend of the river, with the weir in the bend itself. A channel was dug to the lock, creating an island between it and the weir. The weir is also of a different design, being dragged out of the river during high flow, rather than lifted out. ==See also==