Frustratingly these deceptions were often practised by those charged by law with administering the National Water Act, including successive federal and state ministers from both sides of politics and also the Murray Darling Basin Authority, the theoretically independent regulator.

Australia accepted the need for a management plan for the basin in 2007 after the millennium drought. But given clear scientific evidence that an extra 4000 gigalitres of water must be set aside for environmental flows down the rivers, the floundering Gillard government piked. In 2012 it told the MDBA that it must decide on "a  figure starting with a 2". The figure was plucked out of the air.

A few years later, after South Australia secured an agreement from the other states  to stop the mouth of the river drying out, then Water Minister Barnaby Joyce ignored it, rudely telling the SA minister he would always prioritise irrigators over the environment, whatever the legislation said.

The MDBA, which sets the environmental needs of the river, has negligently refused to factor in the impact of climate change and relied on decades-old data. Victorian and NSW state governments have promised but then failed to install water meters  or hire inspectors to  check whether irrigators comply with the plan. The royal commission says that large sections of NSW rivers are a "data-free zone".

The other great fiction is the claim that the rivers can be fixed by investing in new irrigation projects to use water more efficiently.  Farmers with National Party connections have been given hundreds of millions of dollars for projects on their land but the SA commission found that no one bothers to measure if they actually save any water for the environment. When the commission tried to get to the bottom of who was paid how much and why, authorities refused as if it was seeking information on  "stolen plutonium or a terrorist cell". Echoing the Productivity Commission's advice  last year, the royal commission says that these "efficiency projects" should be abandoned and money should be spent on buying back water licences from farmers willing to sell.

There will always be disagreement about the best way to protect the river system and balance the interests of  water users upstream and downstream.  But the commission's key message is to drop the pretence.

After the federal election, the next government should seek clear advice on what environmental flows are needed to save the Murray-Darling. Most likely, the MDBA in its current compromised form is not the body to give it. The new regulators in conjunction with the states should then get cracking and make sure this serious target is actually enforced on the ground.