CSU researchers calling on MBDA, Water NSW to investigate Hume solutions

The 37 crayfish were rescued by NSW DPI Fisheries and they are now being housed at Charles Sturt University's aquatic research facility in Thurgoona.

Fish ecologist Lee Baumgartner said the crayfish were found sitting on the bank of the Murray River, below the dam.

"If the oxygen in the water gets too low, they can crawl out, and get more oxygen from the air than the water," he said.

"They would have dried out and died (if they hadn't been rescued)."

When freshwater ecologist Katie Doyle first saw the crays two Sundays ago, she was alarmed by a "rusty coating" covering their bodies and usually-white claws.

"I've never seen that before - it was like fake tan, it was sticking on my skin," she said.

"So that was an alarm bell for me.

"They also have a natural parasite that lives on them, but there were none on these guys.

"They were very lethargic, but they have bounced back now."

The increased levels of iron and maganese, which the Murray-Darling Basin Authority has attributed to bushfire run-off, is not only causing problems for the aquatic life that lives in the Hume, or water released from it.

Drinking water has been discoloured and smelly - although it has been deemed safe to drink.

Professor Baumgartner said the bushfire run-off could hardly be avoided, but those chemicals were being compounded by a phenomenon that regularly takes place in the dam.

"The dam is stratified, which it does all the time - you've got the warm water at the top and the cold water at the bottom," he said.

"And when that happens, the cold water in the bottom just chews up the oxygen.

Professor Baumgartner disagreed with the MDBA's position that little could be done to prevent the current situation.

"There's stacks that can be done - there's engineering solutions to de-stratify a weir pool," he said.

"For example, they trialled a big curtain at Burrendong Dam on the Macquarie River.

"You can have what they call a multi-level off-take, where the water is released from the top and it goes down a pipe, having different levels set up so that when the lake level goes down it still releases from the top.

"The thermal curtain at Burrendong cost several million dollars ... but an air compressor with a hose (to oxygenate the water), it's not going to cost you much at all - $20,000 to run for a few days.

"There's solutions there, but no one has ever trialled them at Hume - it's quite often just put down to cost."

Professor Baumgartner said a serious review of changes to Hume Dam could have not only ecological, but economic benefits in preventing blue-green algal events.

"Ever since Hume Dam was built, it has stratified," he said.

"Maybe it's time to try one of those solutions.

"Water NSW and MDBA are aware of it, I just don't think there's been a situation where they've wanted to try it."

Dr Doyle acknowledged the importance of Hume Dam to water storage and irrigation but said the ecological impacts were important too.

The cold water at the bottom of the dam - which can be 10 degrees cooler than water at the top, and is released downstream - can stunt fish growth or prevent breeding altogether.

"Murray cod needs between 15 and 18 degrees to spawn, but if it's 13 or 14, that's not good for spawning for native fish," she said.

"That's why we spawn fish in certain areas, because they won't without intervention."

Professor Baumgartner said while there had been water management innovation in the century since Hume was built, little had changed on the ground.

"Dams aren't natural - we created this problem, so we have to fix it," he said.

"It (intervention) may not have helped the chemicals in the water, but it certainly would have helped the oxygen levels.

"The MDBA said there could be fish kills, but it could also just drive all the fish downstream.

"The difference between the fish and the crays is that fish can swim.

"It's about time to give a solution a go, even if it's a pilot."