Western Murray Land Improvement Group (WMLIG) executive officer Roger Knight told ACM that as a result of extensive flooding along the basin throughout Victoria and NSW in 2022, dissolved oxygen levels had dropped well below the normal range of 6-8mg/L.
"[In 2022] we've generally hovered in the Murray River above 0mg/L but below 2mg/L so we've gotten to some really low levels; below 0.5mg/L for about a week in this event," he said.
"For a couple of weeks we've started seeing shrimp come out of the water and congregate near the edge and die, crays are coming out of the water and there have been some fish deaths."
Australian National University Fenner School of Environment and Society Professor Jamie Pittock told ACM the blackwater issues were not unlike what occurred along the river after major flooding events in 2010, 2011 and 2016.
Although this year's event has not been as severe as in the past. In 2010, dissolved oxygen levels in the river near Barham in NSW were undetectable for six months.
"Ironically, one of the issues here is that there's too infrequent flooding, so before development of the rivers the rivers would naturally have flowed on to the floodplain ... every year or every second year and the leaf litter wouldn't get as much of an opportunity to build up," Professor Pittock said.
In 2013, the federal, Victorian, NSW and South Australian governments agreed to implement large scale solutions under the Murray Darling Basin Authority (MDBA) constraints management strategy to 'investigate how water can get to where it's needed'.
"[The strategy] is about the governments working with land holders on the floodplain to purchase flood easements across private property and working ... to relocate or raise or strengthen infrastructure that might go underwater like low lying roads and bridges," Professor Pittock said.
"That's so the environmental water that's being held in big dams ... can be released out in a pulse that fills up the river channel and spills that over onto the floodplain.
"That will all diminish the amount of leaf litter on the floodplain and that would prevent or dramatically reduce these big blackwater events."
Dams such as Burrinjuck, Hume and Eildon are designed to hold back smaller and medium sized floods that previously would have flushed out floodplains, and are used instead to run that water out to supply irrigated agriculture in drier months.
WMLIG's Mr Knight said there was support among river communities for this strategy that could deliver highly oxygenated water to rivers and creeks across the basin.
"A lot of fishermen and others have been really vocal about the need to continue that and to make sure that there's information out there so people can make rational informed decisions about the fact that, you know, it's not new water that's coming from nowhere; if it wasn't coming down as irrigation systems it would be going in the river somewhere," he said.
"It's been overwhelming that people want more water in the landscape, especially people downstream in the rivers at the bottom end of the system."
MDBA's deadline to implement and deliver on the constraints management strategy promises is 2024.
Article Attrition: Ellie Mitchel, Batesmans Bay Post