November 2, 2022
Photo: CMA staff rescue native fish from blackwater in northern Victoria.
Following the recent flooding events across northern Victoria, blackwater and low dissolved oxygen levels in waterways are causing stress or death of native fish in several locations.
Hypoxic (low oxygen) blackwater occurs when oxygen levels in the water drop due to high levels of organic matter (such as twigs, leaves, grass) washing into our waterways and combined with warm weather, it can cause harm to fish and other aquatic species.
Agencies including Department of Environment, Land, Water and Planning (DELWP), Catchment Management Authorities (CMAs), Victorian Fisheries Authority (VFA), Victorian Environmental Water Holder (VEWH) and Traditional Owners are working together to assess risks, this includes active monitoring of dissolved oxygen levels at many waterways and local observations of water quality and native fish.
Where it is safe to do so, the agencies are taking immediate action including moving fish to areas with better water quality, provision of water for the environment in specific areas only when flows return to normal levels, use of aerators to create small pockets of local refuge, translocation of large fish/broodstock to hatchery facilities for breeding or later return to waterways.
The Victorian Fisheries Authority have reported that around 500 native fish, including Murray cod, trout cod, golden and silver perch, have been rescued from the Gunbower Creek system and relocated to areas with good water quality like the Campaspe River. Around 100 native fish and crayfish have been transported to the Arcadia fish hatchery. A small number will be kept as broodstock to assist in restocking impacted waters and the remainder will be returned to the river system once the water quality has been improved.
Unfortunately, many waterways are still experiencing flood conditions which means it is not yet safe or possible to access these areas for assessment and monitoring.
Longer term recovery planning to repair damage to waterway and catchment assets and boost the health of native fish is also underway.
Recreational fishers can help out by contacting the relevant authority if you see distressed fish, including crayfish leaving the water or fish kills:
- Environment Protection Authority Victoria: 1300 372 842
MURRAY CRAYFISH RESCUED ALONG THE BANKS OF THE MURRAY
Along the banks of the Murray River in Echuca and Swan Hill, NSW DPI Fisheries have been working with OzFish Unlimited volunteers to rescue Murray crayfish. Due to poor water quality and low oxygen levels from the recent floods, crayfish have been reportedly exiting the river in droves.
The successful rescue operation saw 255 Murray crayfish rescued from the Murray river. The crayfish will be held at the Narrandera Fisheries Centre until water quality improves and they can be returned to the river.
If you witness any distressed fish, crayfish leaving the water or fish kills in NSW waters contact:
POTENTIAL IMPACTS TO THE MURRAY-DARLING BASIN
The above graphic from Murray-Darling Basin Authority (MDBA) shows potential threats to water quality in the Murray-Darling Basin following the recent flooding events through both Victoria and New South Wales.
The Murray-Darling Basin Authority are working with Commonwealth Environmental Water Holder and Department of Planning and Environment to monitor the conditions of the impacted waterways.
Read more on the MDBA’s website here.
This short video explains the causes and effects of blackwater.
