The Murray-Darling Basin Authority has warned of more mass fish deaths and blue-green algae events throughout the Murray-Darling River system as the peak group representing First Nations issued a plea for the states to stick with the plan.

The MDBA issued a communique on Friday saying the summer outlook from the Bureau of Meteorology was “dire”, and there was a greater than average chance of drier, warmer conditions and an elevated fire danger across the basin.

“We are already seeing the drying of critical aquatic refuges in the north, and water quality issues such as blue-green algae and stratification are becoming more widespread,” the MDBA said.

These were the conditions that led to mass fish deaths at Menindee in January this year.

The MDBA reiterated how important it is to use what little environmental water that remained available to protect critical habitats and maintain water quality.

It has produced a detailed water quality map that will be updated as the drought worsens.

The New South Wales water minister Melinda Pavey has been scathing about environmental water releases and called for the commonwealth to stop them, even though they are usually conducted in conjunction with state water authorities.

Pavey and the deputy premier and nationals leader John Barilaro have threatened to pull NSW out of the plan if their demands are not met. A crucial meeting of water ministers will take place in Queensland on 17 December.

Meanwhile, the peak body representing First Nations from the southern basin has issued a plea for states to stay in the plan, warning that abandoning the plan would marginalise the most vulnerable communities in the basin and endanger the health of the river.

“Campaigns led by irrigators and the NSW National party to derail the basin plan do not represent the interests of all communities across the basin. Governments must listen to all voices in this debate, not just the loudest and most belligerent,” Murray Lower Darling Rivers Indigenous Nations chair and Nari Nari man Rene Woods said.

“Today, rivers like the Baaka [Darling] and Macquarie are in a state of emergency. First Nations people have been marginalised from ownership of land and water. Now our communities and culture are suffering as we watch our waterways in terminal decline,” Woods said.

He said no one pretended the plan was perfect but it was better than no plan at all.

“We need an ambitious basin plan to restore our rivers to health, with strong targets for recovering water for wetlands, billabongs and iconic red gum forests,” Woods said.

Indigenous groups have made some headway in gaining greater acknowledgment and funding to enable them to control water entitlements for cultural flows in the last 12 months but the drought now threatens to set back progress.

Meanwhile, southern irrigators are particularly upset as many sold their high-security water rights during the last drought and general-security water rights have received no allocations at all. Yet the Murray is full and sometimes overflowing its banks as water authorities attempt to meet demand for water further downstream where almonds and other crops are grown.

Farmers carry a coffin with the words ‘Bury the Basin Plan’ as they attend the ‘Can the Murray-Darling Basin Plan’ rally outside Parliament House in Canberra on Monday. Photograph: Lukas Coch/AAP

At the same time southern irrigators are upset about how the river system has been administered in the northern basin which has seen the Darling run dry and the Menindee Lakes emptied. This means there is no contribution coming from this source to the Murray.

There is also deep unhappiness about water being sent to South Australia’s lakes.

These tensions are set to come to a head at the ministerial meeting in Queensland on 17 December.

The ministers will have their first chance to discuss a report by former Australian federal police commissioner Mick Keelty, which has recommended significant changes to the administration of the plan, including the creation of an inspector general. Keelty has been named to the position, but one state, believed to be NSW, has not agreed.

Keelty has been highly critical of the federal agriculture department saying it suffers from inaction, a risk-averse culture and has no clear mission when it comes to water.

He has also warned there has been a “crisis of confidence” in the governance arrangements in the northern basin, which was the focus of his review, and that this has been exacerbated by the historical arrangements and the influence of lobbyists.

The Murray-Darling Basin inspector general Mick Keelty. Photograph: Mike Bowers/The Guardian

For the first time a public official has confirmed there is an NSW Independent Commission Against Corruption inquiry into the administration of water entitlements in NSW following the Four Corners’ report in 2017 which revealed allegations of water theft and allegations of information being provided by government officials to irrigator groups to undermine the Murray-Darling Basin Plan.

There is also likely to be heated debate about NSW’s demand that it be given more time to develop its water-sharing plans. It wants them delayed until the drought breaks.

The current Barwon Darling water-sharing plan is at the heart of the Icac investigation. The rules devised under previous National party ministers are extremely favourable to major cotton irrigators in the northern basin and are blamed by those downstream for the dire state of the lower Darling.

In its communique following the meeting this week the MDBA appeared to signal it would not be backing down on the timetable for water-sharing plans.

“The remaining water resource plans are on track to be assessed for accreditation in early 2020, except for those from NSW,” it said.

“If it is [given more time until the drought breaks], it will only create greater uncertainty and confusion for water users who would then be subject to both commonwealth and state legislation, which is not clearly aligned,” it said

Meanwhile the Australia Institute accused Keelty of pulling his punches.

“The Murray-Darling Basin’s ‘top cop’ fails to identify many publicised examples of maladministration and malfeasance that have occurred during the implementation of the basin plan,” said Maryanne Slattery, senior water researcher at the Australia Institute.

“The report failed to even mention, let alone investigate, some of the most egregious claims of wrongdoing,” Slattery said.

These included alleged rorting of the commonwealth’s $4bn water-efficiency program, allegations that the MDBA drained Menindee Lakes outside its operating rules and the growth of floodplain harvesting which is blamed for the record low inflows into the Darling River.