Water authorities are warning that some waterways might experience low oxygen levels leading to the phenomena known as blackwater, which can kill fish and invertebrates.
Photo by
Julie Mercer
Water authorities have warned of the danger of blackwater events in rivers and streams following widespread flooding across northern Victoria.
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The Murray-Darling Basin Authority has warned that some waterways might experience low oxygen levels leading to the phenomena known as blackwater, which can kill fish and invertebrates.
MDBA environmental management senior director Janet Pritchard said the significant and widespread flooding in the Murray-Darling Basin would see water extending to some floodplains that have not had water on them for several years.
“Hypoxic blackwater events occur as leaf litter and other carbon-based debris is swept into waterways,” Dr Pritchard said.
“As this material is consumed and broken down by bacteria, oxygen can be sucked out of the water, making it difficult for fish and other aquatic animals to survive.
“There are already isolated reports of crayfish exiting floodwaters to escape poor water quality.”
Country News has been shown photographs of yabbies climbing trees to escape murky floodwater.
"With the onset of warmer weather in the coming weeks, water temperatures will start to climb and the possibility of hypoxic blackwater will increase and unfortunately, we could see fish deaths like we did during the 2011 and 2016 floods,” Dr Pritchard said.
“In the past 20 years, large-scale hypoxic blackwater events have been associated with late spring or summer floods, particularly in the Murray, Edward-Wakool, Lower Darling and Murrumbidgee rivers.
“This season the risk will apply to several other systems across the basin in NSW, Victoria and South Australia as well.
“The high flows and widespread flooding will also add nutrients to waterways, which will favour the growth of blue-green algae with warmer conditions.”
The current watch points for potential blackwater events in NSW include: Wakool River, Murray River, Little Merran Creek, Thule Creek and Barber Creek.
NSW Department of Planning and Environment water planning implementation director Allan Raine said dissolved oxygen levels in these areas had been steadily declining over recent weeks.
Dead carp in the Broken Creek at Nathalia on October 25.
The Commonwealth Environmental Water Holder Simon Banks said state and federal environmental water managers were working with industry and local communities to divert very small volumes of good quality water from the main river channel, via irrigation channels, and then diverting it back into creeks further downstream where there is poor water quality.
“These small flows can create localised pockets of better water quality for fish and crayfish to move into,” Dr Banks said.
“This worked well last year and is being used again in the Edward/Kolety-Wakool region, where natural flooding has already resulted in low-oxygen blackwater.
“We are working with local landholders and will avoid delivering water where it will exacerbate the impact of floods.”
Check water supplies
Goulburn-Murray Water is advising residents in flood-affected areas of northern Victoria to check for water quality issues when drawing water from rivers, creeks or the irrigation system.
G-MW emergency controller Peter Clydesdale said floodwater could carry silt and organic material from inundated areas, including dead animals, wastewater (human and animal), crops and vegetation debris.
“If you’re using water supplied by G-MW, monitor the supply source and make alternative arrangements if water quality deteriorates,” he said.
If rural people have concerns about water quality in rivers, creeks or the G-MW irrigation system, phone G-MW on 1800 013 357.
To report potential blackwater events in NSW, call the NSW Fisheries hotline on 1800 043 536.
In Victoria, report fish deaths to the EPA’s pollution hotline on 1300 372 842.
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