There is no alternative but to reach an effective compromise. The basin is the lifeblood of the world's driest inhabited continent, channelled by the Great Diving Range through 3300km of sweeping plains and undulating hills, from Queensland to the mouth of the Murray River in South Australia.
More than two million people live within the basin's 1m sq km, on farms, in towns, and in cities ranging from Toowoomba in Queensland, Dubbo and Wagga Wagga in NSW, Shepparton in Victoria and Renmark in SA.
Its boundaries include the nation's capital, Canberra. The system keeps Australia's fifth biggest city, Adelaide, alive.
The 77,000km of rivers within the basin nurture farms producing more than one-third of the nation's food, from beef, dairying and wheat to fruit, vegetables and wine. Sixteen of its 30,000 wetlands are listed as internationally important.
Its cultural significance is immense: the basin is home to more than 30 Aboriginal nations, who believe their interests - and their potential contributions to its management - have been sidelined.
The underlying issue is simple. There are too many competing demands on the basin's available water, and pressures are increasing.
The MDBA says that for more than a century the system has been controlled by an expanding network of dams, locks and weirs that have altered and reduced flows, changed river temperatures, and affected nutrients and sediments.
Between the 1950s and 1980 water storage capacity increased seven-fold. The federal science agency CSIRO says it now exceeds the average annual flow of all rivers in the system and is more than double the average natural flow to the sea.
The total flow of water at the mouth of the Murray, spilling to the ocean through Lake Alexandrina south of Adelaide, has been cut by about 60 per cent. The river stops flowing into the sea 40 per cent of the time: in its natural state this happened only once in a century.
The basin's ecosystems have been hammered, hitting native fish and birds. Wetlands and forests have suffered, and toxic algal blooms have mushroomed across its waters.
Salt has spread like a cancer, killing land, plants and fauna.
Finding answers has been a nightmare maze of environmental, economic, social and political storms, so far largely ineffective and extremely costly: an estimated A$25 billion ($31.4 billion) has been spent on the basin over the past 15 years.
The upstream states have always sought water security in massive storage systems. Downstream users demand that more water is allowed to flow, especially in SA where tens of thousands of tonnes of chemicals are used every year to keep Adelaide's drinking water safe. Salt levels exceed World Health Organisation standards for about 10 per cent of the year, with predictions this will rise to 40 per cent within two decades.
Progress on a deal between federal and state governments has been glacial. An agreement was first adopted in 1985 but not enacted for a decade.
Finally, in late 2010, the MDBA released a draft plan proposing to reduce existing water allocations and allow more water to flow to the Murray's mouth in a bid to flush the system, attack salinity, improve water quality and repair ravaged ecosystems.
The original plan, proposing reductions of up to 45 per cent in allocations in some areas, triggered howls of outrage and predictions that entire industries and communities would be obliterated.
In its fourth version, the draft plan recommends increasing water flows by 2750GL, with flexibility for adjustments. This was controversial enough, rousing alliances of farmers, horticulturists, irrigators and local councils.
But new modelling commissioned by the federal-state ministerial council on the basin has put a new cat among the pigeons. This shows that lifting the flow of water by an extra 450GL, to 3200GL, would be far better for the health of the system.
This was applauded by conservationists and SA, which has threatened High Court action if at least that amount is not allowed to run back into the system.
NSW and Victoria have rejected the modelling outright, warning of massive social and economic disruption and "substantial and sustained flooding of towns and private land".
Saving the basin remains a political migraine for Australia.
The Murray-Darling Basin: a nation's lifeblood:
*Stretching more than 3300km from Queensland to South Australia, the 1m sq km basin is home to more than 2 million people.
*Its 77,000km of rivers embrace 30,000 wetlands, some of international significance, floodplains and fragile ecosystems.
*Sprawling across much of Queensland, New South Wales, Victoria and SA, the basin drains one-seventh of continental Australia and produces more than one-third of the nation's food.
*Beef, sheep, dairying, cropping, horticultural industries support major industries including transport and manufacturing, extending the basin's economic importance beyond its boundaries.
*The basin is important culturally, and its health important physically and spiritually to more than 30 Aboriginal nations living within it.
Shooting the political rapids
*A national management plan to cross state borders becomes inevitable as the basin's rivers slow to a relative trickle, ecosystems decay, water quality plummets, salinity and toxic algae choke its waters.
*The first agreement in 1985 takes decade to enact, with few gains.
*A draft plan is released to controversy in 2010, proposing cuts in water allocations to increase water flow and restore the system's health.
*The plan is amended as competing interests continue to clash, recommending an extra 2750GL be released to boost environmental flows.
*Amid angry exchanges over the latest proposal, new modelling finds that an even higher extra release of 3200GL would be far better for the system.
*Despite bitter exchanges and threats of High Court action, the federal Government hopes to reach a deal by the end of the year.
