Antinuclear

The sight of more than a million fish floating belly up on the Darling River at Menindee has thrown doubt over the management of the Murray-Darling Basin.

Experts say irrigators are taking too much water from the system, and the Murray-Darling Basin Authority has mismanaged water flows.

But New South Wales Water Minister Niall Blair says drought is to blame.

With more fish likely to die, here’s what we know about the mass deaths and what some independent experts have had to say.

Where are fish dying?

A million fish were found dead at Menindee Lakes last week.

It’s a series of seven lakes fed by the Darling River, about 90 kilometres south-east of Broken Hill in western New South Wales. It’s believed to be one of the largest fish kills ever recorded in Australia.

Then a smaller kill of about 60 fish was reported at Lake Hume yesterday, on the NSW-Victoria border.But the cause of that kill is still unclear.

What killed the fish?

A variety of factors were at play at Menindee. Water levels were very low, the system had stopped flowing, and temperatures were high after a long spell of hot weather.

This created ideal conditions for blue-green algae (cyanobacteria) to grow, and it “bloomed” out of control.

But it wasn’t the algae that killed the fish.

A cold front hit the region, which dropped the water temperature in the river, killing the algal bloom.

The bacteria that feeds on dying algae then exploded out of control, and sucked all the oxygen from the water.

When the oxygen levels dropped too low, the fish drowned.

So who or what is to blame?

The blame game began almost immediately after the Menindee fish kill was reported.

• Farmers Rob McBride and Dick Arnold, whose video of dead Murray cod went viral, pointed the finger at cotton growers and politicians.

  But others blame mismanagement by the Murray-Darling Basin Authority (MDBA), and the NSW Government blames drought.

  The big question is: why was the river in such a state that a blue-green algae outbreak of this scale could occur?

  Here’s what four experts working in the fields of river ecology, policy, management and economics told us.

  1. Expert in water economics, environment and policy

  Adjunct Professor John Williams from the Australian National University said you couldn’t blame the drought.

  “To manage a river you’ve got to be able to manage it through a drought without killing all the fish,” Professor Williams said.

  “We didn’t put enough environmental water aside, and then we’ve continually eroded the little we did allocate with the recent amendments both in the north and to the south.”…….

  2. Expert in conservation biology, wetland and river management

  Professor Richard Kingsford from the University of New South Wales said farmers and irrigators were suffering from the drought, but water management was a big issue.

  “Certainly the drought is a contributing factor. The bigger issue is that this has been coming for a long time in the Darling,” he said.

  “Over the last 20 or 30 years, we’ve reduced flows coming into the Menindee lakes from upstream and down the Darling by almost 50 per cent. And it means there’s less water in the river than there used to be.”

  As well as extracting water from the river, licences allow some irrigators to capture overland flows.

  Overland-flow capture means diverting rainwater into storage before it reaches the river, which in turn leads to less water entering the system.

  “Some cotton growers in the Darling River tributaries have managed to capture some of the water in the recent rains that have occurred, and that’s part of the licencing system that allows them to do that, to harvest those flows,” he said.

• 3. Expert in water policy reform

  Professor Michael Young from the University of Adelaide said the Murray-Darling Basin Authority had failed to plan for lean times.

  “We’ve put a lot of effort into debating what is called the ‘sustainable diversion limits’, which is working out the maximum amount that can be taken when the tank is full,” he said.

  “We’ve put very, very little effort into working out how to manage times of low flow and who’s responsible for that.”………

• 4. Expert in ecology, management and restoration of aquatic ecosystems

  Professor Robyn Watts from Charles Sturt University said that drought, climate change and mismanagement had all contributed to the state of the river…..https://www.abc.net.au/news/science/2019-01-16/what-caused-menindee-fish-kill-drought-water-mismanagement/10716080