The Murray–Darling Basin is an area of land in the interior of southeast Australia. It includes the drainage area of the Murray River, which is Australia’s longest river, and the Darling River, a river that flows into the Murray and is Australia’s third-longest river. The Basin includes six of Australia’s seven longest rivers and covers about one-seventh of the country’s land. It is one of Australia’s most important agricultural areas, providing one-third of the nation’s food supply. The Basin is located west of the Great Dividing Range and drains southwest into the Great Australian Bight. It covers most of the states of New South Wales and Victoria, the Australian Capital Territory, and parts of Queensland and South Australia.

The Basin is 3,375 kilometers long, with the Murray River itself being 2,508 kilometers long. Most of the Basin’s area, which is about 1,061,469 square kilometers, is flat, low-lying, and far inland. It receives little direct rainfall. The rivers in the Basin are generally long and slow-moving, and their water volume is large compared to other rivers in Australia.

The Snowy Mountains Scheme helps ensure a steady water supply to the Murray–Darling Basin. It provides about 2,100 gigaliters of water each year to support Australia’s irrigated agriculture industry. This industry is worth about A$3 billion annually and contributes more than 40% of the total value of Australia’s agricultural production.

The original inhabitants

The Basin was once home to many Aboriginal people who lived traditional lifestyles and had unique cultures. Over time, these ways of life changed as Europeans arrived. Some Aboriginal people were killed directly by settlers. Although some groups, like the Maraura near the Rufus River above Renmark and the Tanganekald near The Coorong, tried to resist, they were eventually killed, forced to leave their lands, or died from diseases.

Native fauna

The Murray–Darling Basin is home to many native animal species. While the exact numbers are not fully known, scientists have made an educated guess about the number of these animals and how their populations are doing. The study found the following:

• 80 species of mammals, with 62 no longer living and 10 at risk of disappearing
• 55 species of frogs, with 18 at risk of disappearing
• 46 species of snakes, with 5 at risk of disappearing
• 5 species of turtles, with none at risk of disappearing
• 34 species of fish, with up to half of them either in danger or needing special protection

Historical records show that fish used to be very plentiful in the Basin and served as an important food source. During floods, fish often gathered in shallow water across the floodplain. Today, there are about 24 native freshwater fish and 15–25 marine and estuarine fish species in the Basin, which means the variety of life is much lower than before.

In December 2018 and January 2019, two large fish deaths occurred in the Basin. The first event involved about 10,000 fish, and the second involved hundreds of thousands of fish. The affected species included Murray cod, golden perch, silver perch, and bony herring. Some people said the deaths were caused by WaterNSW draining most of the water from the Menindee Lakes, leaving only 2.5% of the original water. After the first fish death, both the Department of Primary Industries (DPI) and WaterNSW said the ongoing drought in Australia was to blame. However, the DPI later said the second fish death was caused by a sudden drop in temperature disrupting an algal bloom.

In March 2023, millions of fish were found dead along the Darling River near Menindee after a heatwave. As cleanup efforts began, police said the cause was naturally occurring hypoxic blackwater. Early tests by the New South Wales Environment Protection Authority (EPA) took water samples from six sites, but these tests were criticized for not being thorough enough. Later, the New South Wales government declared the fish deaths a "pollution incident," giving the EPA more power to investigate. Earlier tests were said to focus mainly on protecting public health.

Introduced species

Four types of carp were placed into fish dams. After that, they moved into river systems and spread quickly. People may have helped them spread by using small carp as live bait, which is against the rules. These fish move easily, reproduce quickly, and can live in very shallow water and in water with very low oxygen levels.

Carp cause problems because they suck up gravel from the riverbed and take the food from it, then return the rest to the water. This action stirs up sediment, which makes the water quality worse. A project to create carp that cannot have babies shows hope for removing carp from rivers.

Cane toads have been found in the upper parts of the Darling Basin, and some have been seen farther down the river system. These toads compete with native frogs and are poisonous to native animals that eat them.

Phyla canescens has taken over wetlands and floodplains with heavy clay soil in the Murray–Darling Basin, harming native plants. This plant grows best in areas that are flooded sometimes but cannot outcompete grasses and sedges in places that are flooded more often.

Physiography

This area is part of the East Australian Basins division and includes the Naracoorte Platform and Encounter Shelf sections.

The total water flow in the Murray–Darling Basin from 1885 to today averages about 24,000 gigalitres (24,000 hm³; 19,000,000 acre⋅ft) each year. This is the lowest average among the world’s major river systems. About 6.0% of Australia’s total rainfall falls into the Basin. In most years, only half of this water reaches the sea, and in dry years, even less does. The total water flow in the Basin has varied greatly over time, from 5,000 gigalitres (5,000 hm³; 4,100,000 acre⋅ft) in 1902 to 57,000 gigalitres (57,000 hm³; 46,000,000 acre⋅ft) in 1956. Even though the Basin is large, the water movement in its rivers varies a lot.

These waters are divided into four types:

• The Darling and Lachlan basins. These rivers have very different water amounts each year. The smallest yearly flow is often as little as 1% of the average, while the largest can be more than ten times the average. Many rivers in these basins can stop flowing for months or even years in dry areas. Floods in northern parts usually happen in summer due to monsoonal rain. In most areas, high or low water levels often start in winter and last until autumn. High water use for farming and mining has greatly affected these rivers.

• The southwestern basins (Campaspe, Loddon, Avoca, Wimmera). These areas get most of their rain in winter, with less variation in rainfall compared to the Darling or Lachlan basins. However, the old and poor soil means very little water flows into rivers (about one-tenth of similar areas in Europe or North America). Runoff is highly variable, and many lakes in these basins often dry up. Most water flows in winter and spring. Without large dams, these rivers are often dry in summer and autumn.

• Some small areas in South Australia, like the Angas River near Strathalbyn and the Finniss River further west, are part of the Murray–Darling Basin. These areas lead to Lake Alexandrina, a lake at the end of the Murray system. The Angas River often dries up in summer because of high water use. The Finniss River flows into Lake Alexandrina year-round, but it stopped flowing for several years during a drought in the early 2000s due to a dam.

• The Murray, Murrumbidgee, and Goulburn basins (except the Broken River, which is similar to the southwestern basins). These areas have rivers that start in high mountain regions with young, fertile soil. This means more water flows into rivers compared to other parts of the Basin. Even though rainfall varies a lot, the water flow is more stable. These rivers rarely stop flowing, with the smallest yearly flow being about 30% of the average and the largest about three times the average. Water levels usually peak in spring due to melting snow and drop in mid-autumn.

The two main rivers in the Basin, the Murray and Darling, carry water from the high eastern mountains and flow west and south through dry, flat areas. This often creates wetlands, such as The (Great) Cumbung Swamp, at the end of the Lachlan and Murrumbidgee Rivers. However, water is diverted for drinking and farming since the 1890s. Today, 4 major reservoirs, 14 locks and dams, and 5 coastal barriers control the water flow in the Murray–Darling. Studies show that about 13,000 gigalitres (13,000 hm³; 10,500,000 acre⋅ft) of water in the Basin can be used. Of this, 11,500 gigalitres (11,500 hm³; 9,320,000 acre⋅ft) are used for farming, industry, and homes. Farming uses about 95% of this water, including for growing rice and cotton. Scientists in Australia debate this because farming uses so much water in an area that already has very little water available. These irrigation systems need reliable water, not the unpredictable flows of the Murray–Darling. During "the Big Dry," a severe drought in the early 2000s, many rivers and streams, like the Murray–Darling, stopped flowing. The Basin has over 30,000 wetlands, with 11 protected under the Ramsar Convention for their international importance.

• Yarrawonga Weir

Murray–Darling Basin Initiative

The Basin covers five states and a territory. According to the Constitution, these governments are responsible for managing water resources. The River Murray Commission was created in 1917. The River Murray Waters Agreement, which did not include Queensland even though about a quarter of the Basin is in that state, made the commission an advisory group with no power to enforce rules. For many years, the commission focused only on water quantity until salinity became a problem. This led to small changes in 1982, when water quality was added to the commission’s duties.

Soon, it became clear that a new system was needed to manage the Basin effectively from a national perspective. The Murray–Darling Basin Agreement was first adopted in 1985 but did not gain full legal status until 1993. This Agreement created new organizations under the Murray–Darling Basin Initiative, including the Murray–Darling Basin Ministerial Council and the Murray–Darling Basin Commission.

The Murray–Darling Basin Authority (MDBA) was formed in 2008 to manage the Basin in a way that balances the environment and sustainability. The MDBA is responsible for creating and overseeing a legally-enforceable management plan. In October 2010, the MDBA released a draft Murray–Darling Basin Plan (MDBP) for public feedback. On 22 November 2012, Tony Burke signed the plan, which passed the Australian Parliament’s disallowance period on 19 March 2013.

The MDBA’s draft plan, titled the Guide to the Proposed Murray–Darling Basin Plan, was released in October 2010 as the first step in a three-part process to address issues in the Basin. The plan responded to the 2000s Australian drought and aimed to protect the Basin’s long-term ecological health. This included reducing water allocations and managing environmental flows for tree growth. The plan set limits on water use, established goals for water quality and salinity, created systems for trading water efficiently, required state water plans, and aimed to improve water security for all users. It also sought to minimize social and economic effects while achieving environmental goals.

After the Guide was released, many people in rural areas expressed concerns about the plan during public meetings. Over 5,000 people attended a meeting in Griffith, where the mayor said the plan would harm communities in the Murrumbidgee valley. Other groups, like the Victorian Farmers Federation and Wine Group Growers’ Australia, shared similar concerns. However, groups such as the Australian Conservation Foundation and Environment Victoria supported the plan.

New legal advice from the Commonwealth government changed parts of the plan. The government stated the plan must balance environmental, social, and economic impacts of water cuts. Environmentalists and irrigators in South Australia argued the MDBA should follow its original water limits.

In October 2010, a parliamentary inquiry was announced to study the plan’s economic effects. The Water Minister, Tony Burke, said it was unlikely there would be a High Court challenge to the plan, despite confusion over new legal advice. In response to concerns that the MDBA prioritized environmental goals over social and economic needs, Burke shared updated guidance on the Water Act. A legal expert, George Williams, questioned the government’s interpretation of the law, suggesting it might face legal challenges.

In November 2010, the MDBA said it might delay the final plan until early 2012. The then-MDBA chairman, Mike Taylor, assured the public that more work would be done to study the plan’s effects on communities. He later resigned, reportedly believing the plan should prioritize environmental goals, which conflicted with the Gillard Government. He was replaced by Craig Knowles, a former New South Wales Planning Minister.

In late May 2012, the revised plan was sent to state water ministers. It did not change the recommendation to reduce water entitlements by 2,750 gigalitres. After discussions between the Commonwealth and state governments and feedback from the public, the Basin Plan became law in November 2012 and is now being implemented.