River

Murray Cod threatened by drought

Friday 14 September, 2007
A safety net to avert the deaths of Murray Cod has been triggered by the Goulburn Broken Catchment Management Authority (GB CMA).

A safety net to avert the deaths of Murray Cod has been triggered by the Goulburn Broken Catchment Management Authority (GB CMA).

Officials say increased levels of the tiny aquatic water fern, Azolla (which is also known as Duck Weed) has depleted oxygen levels to dangerous levels in the Broken Creek.

Azolla flourishes in low-flow conditions, covering the water with a velvety green carpet. If levels build up, it reduces dissolved oxygen levels in the water, which the fish depend on to survive.

Azolla caused the deaths of 160 fish in a single episode in 2002 and the GB CMA Environmental Water Flow Co-ordinator Geoff Earl said the authority and Goulburn-Murray Water have been actively managing flows to avoid further events which risk one of the biggest cod breeding habitats in Northern Victoria.

Fish start to get stressed once there is less than four milligrams per litre (mg/l) of dissolved oxygen in the water. Once the levels fall below two mg/l, fish are in a high-risk situation. Dissolved oxygen levels this winter and spring have dropped as low as one mg/l.

The GB CMA reacted by organising release of 1000 megalitres of the Goulburn water quality reserve down Broken Creek to flush out the Azolla and restore balance.

"It's a dynamic situation," Mr Earl said. "Things can change very quickly. Once the dissolved oxygen level dropped we needed to act promptly to protect the cod population.

"We're mitigating the risk by carefully targeting the water used. We still have Azolla growing but we have averted any tragedies. This season is very difficult for everyone and we all need to be extremely water efficient."

The water which has been used will be returned to the Murray River at Barmah and reused in the Murray system.

Release Ends 

For more information contact:
Geoff Earl at (03) 5820 1128 (first choice) or on mobile 0429 381 887
or Dianna Malcolm (Impress Publicity) 0n 0419 483 763.