The ALP is preparing to use federal powers under the Water Act and its influence with the two Labor-controlled basin states to drive better environmental outcomes if it wins government in May.

The opposition spokesman on the environment and water, Tony Burke, told Guardian Australia he would immediately convene the ministerial council and outline what he wants to achieve.

“If the states refuse to cooperate, I will look at powers in the Water Act,” he said.

So far the Murray-Darling Basin Authority (MDBA) has not used all its powers, preferring to work collaboratively with the states. However the act gives the MDBA the authority to take over the planning powers of the states in relation to the river system as well as allowing a greater role in enforcement.

Since Guardian Australia investigated the Murray-Darling in March 2018, the health of Australia’s greatest river system, and the $13bn plan to save it, have been thrust into the centre of the national political debate.

The drought that began to unfold in early 2018 has become prolonged and highlighted inadequacies in the plan.

The most dramatic warning has been the deaths of hundreds of thousands of fish at Menindee. The deaths of 40- and 50-year-old Murray cod, which survived the millennium drought of the early 2000s but perished this time around, horrified Australians and raised serious questions about the management of the river.

There are now marked policy differences between the Coalition and Labor at state and federal level over what should happen next under the plan, though both major parties remain committed to retaining the plan itself.

The question is: can the basin plan be reformed – and the remaining $4.5bn be spent constructively – without the key stakeholder states and the farming lobby pulling out of the plan?

Hundreds of thousands of fish died at Menindee over the summer. Photograph: Graeme McCrabb

A bare-minimum plan

The Wentworth Group of Concerned Scientists has warned from the outset that the environmental water recovery target of 2750GL in the plan was a political compromise and is a bare minimum to restore the health of the Murray-Darling River.

Since then, serious management failures have led to a systematic weakening of reforms and undermining of the plan, they say.

“Without major changes in implementation, it is almost certain that the basin plan will fail,” the group has warned in numerous submissions.

The group’s spokesman, Prof Jamie Pittock, said there have been improvements in enforcement in New South Wales after the ABC Four Corners report in July 2017, which sounded the alarm over allegations of water theft by cotton irrigators in the north of NSW.

But he said: “The major part of the problem – bad rules in water-sharing plans – remain. NSW and Victoria haven’t changed their attitude towards fixing them.”

Inquiries point in the same direction

The most scathing and comprehensive criticism of the basin plan was delivered in February by a South Australian royal commission. It found officials at the MDBA and in government were guilty of maladministration, negligence and unlawful actions in drawing up the multibillion-dollar deal to save Australia’s largest river system.

The commissioner, Bret Walker SC, warned the plan’s failure to take account of climate change was “potentially catastrophic”.

While the Morrison government and the MDBA dismissed the findings (they had refused to participate in the inquiry) the royal commission heard from many of the leading scientists in the field. There was a distressing consensus in their assessments.

Many of its findings were backed up by the Productivity Commission’s five-year review, albeit in more temperate, bureaucratic language.

“Deficiencies in the way that governments have approached implementation of the plan have caused considerable concern in many basin communities. This has left a legacy of community distrust, which the commission considers is a risk to effectively implementing the next phase of the plan,” it said.

In the fine print, it noted the poor enforcement by states, that new plans to deliver on water sharing were way behind schedule, that programs to find water savings in other ways were highly ambitious and risky, and the MDBA’s evaluation frameworks were inadequate.

Then there were two reports – by the Academy of Science commissioned by Labor, and the Vertessy report commissioned by the government – in the wake of the fish kills. Both concluded that low flows had been responsible for the conditions that led to the mass deaths.

Australian National University professor and chairman of the Academy of Science’s panel, Craig Moritz, said his review found “there isn’t enough water in the Darling system to avoid catastrophic outcomes”.

“This is partly due to the ongoing drought. However, analysis of rainfall and river flow data over decades points to excess water extraction upstream,” he said.

A common theme in all of these reports is that flows in the northern part of the system are dramatically reduced compared with historical records, and it cannot be explained solely by drought.

The likely causes are climate change, which is changing rainfall patterns, and overextraction by irrigators – possibly in breach of the rules and floodplain harvesting, which involves diverting overland flows into private storages before it even reaches the river.

A study by the MDBA identified the problem. From 1990 to 2017, a period which covered the millennium drought, “Some individual flow events in the post-2000 period were seen to be very heavily attenuated in both the Collarenebri-to-Walgett and (particularly) the Walgett-to-Brewarrina reaches, contrary to the established pre-2000 trend,” the study said.

In other words, too much water was being diverted from the river.

But facing up to this new reality is proving difficult.

The Wentworth Group of Concerned Scientists argue that the plan can be salvaged but requires governments and regulators to recognise its weaknesses and put the environmental objectives of the plan ahead of politics.

Irrigation canals and cotton fields on Darling farms outside Bourke in NSW. Photograph: Mike Bowers/The Guardian

One step forward, two back

Over the past 12 months, there have been developments that are both positive and negative.

In the wake of the fish kills, Labor, Greens and minor parties joined forces to make one important change: an amendment that will lift the cap of 1500GL on water that can be bought back from farmers.

The cap had been put in place by the Abbott government in 2015 under pressure from the Nationals who feared the economic impact of more buybacks on rural communities.

But the change will only be relevant if the government of the day calls more tenders to buy back water or if other measures to reclaim water for the environment, such as the supply projects like Menindee Lakes are unsuccessful, forcing a government’s hand.

Burke said the cap on buybacks was never part of the original Murray-Darling Basin Plan.

“By removing the cap on buybacks, Labor is removing a legislative barrier to providing more water for the basin, if that is what is needed,” he said.

The more serious threats to realising the environmental outcomes are two amendments to the plan, supported by the government and opposition, which reduce the amount of water available for the environment.

The plan always envisaged there could be changes, but the two changes – a 70GL cut to the environmental water target in the northern basin and agreement to allow 605GL of water to be recovered in the southern basin through efficiency projects – are controversial.

Both have drawn almost universal criticism from scientists but were supported by the MDBA and by both major parties.

The 70GL is a straight cut that reduces the environmental water recovery target by about 31,000 Olympic swimming pools.

“I guess I was surprised by the figure. But the reality is the plan falls over if you do not support the independent process,” Burke said, explaining his decision to support the government.

But since the Menindee fish deaths, he said he would “not be surprised if MDBA review the 70GL cut”.

The 605GL adjustment in the southern basin is more complex.

The idea is that environmental outcomes equivalent to this amount of flows can be achieved by using water more efficiently often through building river infrastructure or removing it.

The problem is knowing whether the projects will work.

The Productivity Commission described the supply measures projects, as they are known, as “highly ambitious” and rated the risk of failure as “high”.

The Menindee Lakes project, to reduce evaporation by shrinking the lake system, is a case in point.

If the project fails to deliver on its 105GL of evaporation savings, it will mean a shortfall in environmental water that needs to be made in 2024.

Then there is the glacial progress by the states in implementing key commitments under the plan. NSW has been slow on its new water resource plans, leaving in place old plans like the Barwon-Darling water-sharing plan, which have been roundly criticised for allowing pumping by irrigators during low flows at the expense of the environment.

Victoria is under fire for its failure to remove or rebuild bridges and roads and other assets that currently prevent the commonwealth environmental water holder from flooding the upper flood plains, which is critical for endangered ecosystems such as red gum forests.

“If I win the election, I would want to get the ministerial council together as quickly as possible,” said Burke. “One of the things we need is a clear work plan for constraints removal, particularly in Victoria.

“I am determined that I will get constraints removed and I am frustrated by the lack of progress. I would prefer a consensus approach but failure to remove them is not an option.”

Burke said he also expected the states to take notice that water-sharing plans underpin the reforms and there will be “no tolerance” for plans that subvert them.