A new fish kill in the Murray River is not as severe as initially believed, as fears of more fish deaths increase amid soaring temperatures

This article is more than 1 year old

This article is more than 1 year old

The New South Wales government will install aerators at various sites across the state amid fears of more fish kills as temperatures soar above 40C in the Murray-Darling Basin.

A new fish kill event at Lake Hume was downgraded to 60 dead fish from 1,800 after authorities from the Department of Primary Industries arrived to investigate.

The office of primary industries minister, Niall Blair, on Tuesday initially suggested some 1,800 fish had died in Lake Hume, which is part of the Murray River system.

But his department subsequently said an investigation had found “approximately 60 dead carp were located in the water” near a boat ramp.

“A cause of the fish kill has not yet been determined, however, there are no algal or dissolved oxygen issues noticeable,” the DPI said in a statement. “Fishing mortality is one potential cause.”

Fears of more fish kills came as temperatures soared above 40C in the Murray-Darling basin and the Murray-Darling Basin Authority (MDBA) convened an urgent meeting of experts to discuss what can be done to alleviate conditions in the river system.

It follows an incident last week in which more than 1 million fish were reported to have died at Menindee Lakes, including 70-year-old Murray cod, which are listed under commonwealth law as a vulnerable species.

On Tuesday, Blair visited Lake Keepit near Tamworth, the site of another major fish kill two weeks ago, to announce plans to install the aerators.

This fish kill is a tragedy – but it is no surprise Read more

The aeration technology will be installed at Menindee Lakes on Wednesday, Lake Keepit on Thursday and at Lake Burrendong next week.

“Aeration is not a silver bullet solution but it does provide localised areas where fish can get more oxygen, which ultimately gives them a better chance of surviving,” Blair said.

The solar-powered aerators will run at night when rivers are at most risk of suffering oxygen depletion.

“Unfortunately the conditions we’ve seen across NSW are leading to more and more fish kills, which are caused by algae blooms, black water and oxygen depletion from Port Macquarie and Lake Burrendong to Keepit and Menindee,” he said.

Speaking after Tuesday’s meeting, Phillip Glyde, the chief executive of the MDBA, said authorities had been working hard over the last decade to repair the damage wrought from 100 years of over-allocation of water in the Murray-Darling river basin.

He defended the management of the system, particularly the decision by authorities to draw water from Menindee Lakes ahead of other catchment areas. It made sense to draw water from Menindee Lakes ahead of the Dartmouth and Hume dams, he said, because those dams don’t have the high evaporation rates of the Menindee Lakes.

He said the NSW government’s decision to begin installing aerators would only have a limited impact.

Glyde said all options were being considered to save current fish stocks, including relocating Murray cod to areas of the river system that were not as stressed. However, the likelihood such a scheme being successful was low.

He said he did not know where the figure of “one million” dead fish came from, because nobody had counted them yet.

Appearing on the ABC on Tuesday, he said climate change was making it more difficult to manage the system.

“We know the climate is changing,” he said. “That has equal impact on irrigators as well as environmental water holders. We can’t predict precisely where those impacts might be. So, that’s another factor.”

When asked if irrigators in northern NSW were complying with their water allocations, Glyde said it had been a problem in the past and it had been difficult to measure of people are telling the truth or not.

“What we found a few years back is that the compliance system – the rules, actually, even though they are good rules – they weren’t necessarily being followed,” he said.

“So the New South Wales government, in particular, has picked up the ball and run on this. There’s a new regulator in place in New South Wales, the Natural Resource Access regulator. They have done a great job. We’ve seen convictions.

“[But] the size of what is likely to be taken illegally or not recorded is relatively small. It wouldn’t be seen as a cause for this fish kill.

“The system, in order to have confidence that we’re getting in top of the problems of the Murray-Darling Basin, people have to have confidence in the compliance regime, the regulatory regime. That’s been restored to the system at the moment. We are working hard on that.”