It's now five years since $13 billion was allocated by the federal government to save this critical, precious river system and the surrounding environment. Yet, little has been done to alleviate the intense competition over access to water, nor to provide clear data for good management of the Murray-Darling Basin's water flows. In fact, as revealed on Monday night's Four Corners program, there is much we don't know about water taken from the basin's rivers. And, NSW and Victoria are dragging their feet – arguing against the buyback of water for the environment and undermining the environmental provisions of the Basin Plan.

How did it come to this? Last century, the waters of the Murray-Darling rivers were notoriously over allocated by overzealous government water agencies. So many dams were built by tax payers that they could capture 130 per cent of the average annual flow of all the system's rivers. But building dams doesn't get you more water in the same way that opening a bank account doesn't get you more money.

Meanwhile, we seem to have forgotten the dire state of the environment that drove the reforms. Forests of river red gums, black box eucalypts and coolibah trees dead, denied the water flows they relied on by irrigation. Waterbird numbers have plummeted, half the native fish species are now threatened, blue-green algal blooms are increasing, and the Lower Lakes was once taken over by sulfuric acid and salinity.  

The Millennium Drought, in 2002-2009, exposed the basin's fragility. Country towns ran out of water and irrigators bulldozed fruit trees, prompting the federal takeover of the Murray-Darling with a new Water Act 2007, under prime minister John Howard, supported by the then Basin Plan architect, water minister Malcolm Turnbull. The Plan was adopted in 2012 by Julia Gillard's government, resulting in an independent national Murray-Darling Basin Authority, deftly side stepping state governments' Constitutional responsibilities for water.

More than $13 billion was put on the table to fix the river system's many problems — almost half of which was allocated to improving irrigation efficiencies and giving saved water back to the environment, and almost a quarter to buying back water for the environment from willing irrigators. Wind the clock forward to today. The federal government, under pressure especially from the NSW government, has introduced policy changes that are threatening to kneecap the plan, beginning with capping the buyback of water for the environment. Now, achieving environmental flow targets seems highly unlikely. And, even well-intended water buy-backs are coming at high price. 

Cracks in the Basin Plan could be filled and the 2012 deal could still be realised to Australia's benefit. But, this will take tough policy decisions and strict implementation. It means finding out exactly how much water we are using and making sure no environmental water is used for growing crops. It also means no spurious rationales for reducing environmental water targets. Considerable taxpayers' dollars were invested in this deal to make the Murray-Darling Basin healthy. Only a concerted state and federal commitment to the original plan will prevent us squandering the opportunity to deliver sustainability for the Murray-Darling.