Nationals, Greens rock the boat on Murray Darling plans

Dean Lewins/AAP PHOTOS

Proposed reforms to managing Australia's most complex river system are already making a splash, with water buybacks diving into controversy.

Environment Minister Tanya Plibersek introduced amendments to the Murray Darling Basin plan to parliament on Wednesday following revelations it would fail to hit its 2024 water recovery targets.

The scheme outlines the amount of water that can be taken from the ailing basin each year and aims to return 450 gigalitres of additional water to the environment by June 2024.

The new plan will push this deadline to December 2027 and includes more options and funding to deliver the remaining water, such as through voluntary buybacks.

Ms Plibersek said the amendments would ensure the plan was delivered in full as the basin faces a 30 per cent reduction in its flow by 2050 due to climate change and drought.

"This plan delivers more time, more money, more options and more accountability," she told parliament.

The Greens support water buybacks but want more stringent oversight mechanisms and rolling targets to ensure the water earmarked for the environment is recovered this time.

Greens senator Sarah Hanson-Young said the minor party, which holds the balance of power in the Senate, would not tick off on the plan in its current form.

"We want to see what water will be delivered, a promise for water to be delivered before the next election and we want a guarantee the full 450 gigalitres will actually be there by 2027," she told AAP.

But the Nationals remain opposed to buybacks, saying it would jack up water market prices and have a flow-on impact on the agriculture sector.

Opposition water spokeswoman Perin Davey said temporary water prices had already gone up and that the cost of water spiked whenever the government entered the market.

"There is a grave fear amongst the irrigation communities about what impact this will have on farm profitability, on regional employment and ... on the cost of producing our food and fibre," she said.

While maintaining her opposition to buybacks, Senator Davey said the government could still utilise 225 gigalitres left over from the buyback cap that was agreed in the original plan.

"If the government is honest when they say buybacks is a last resort, they can actually achieve it under that cap without having to scare the horses," she said.

Some state governments also oppose buybacks.

Ms Plibersek hasn't said how much the government would set aside for buybacks, saying revealing the details could distort the water market.

The Nationals and the Greens teamed up in the Senate to force the government to produce documents - including briefing notes, emails and advice - from the department that informed the minister's decisions about the legislation.

The government has until September 14 to table the documents or explain why they're being withheld.

A Senate inquiry into the bill is expected to be set up on Thursday.

But a reporting date remains a point of contention with Senator Davey wanting the committee to visit the affected regions and the government pushing for the legislation to be passed by December.