Mass fish kills in the Darling River at Menindee in NSW and at Kangaroo Lake in Victoria have alarmed scientists and local communities.
Climate change, poor river management, and altered floodplain usage are factors that contributed to the deaths of millions of fish.
Experts say immediate action is needed to protect Australia’s river ecosystems.
What caused these tragedies?
Up to 20 million fish died at Menindee last week due to low levels of dissolved oxygen in the water, known as hypoxic blackwater, which was exacerbated by weather extremes, authorities said.
And on Sunday, thousands of fish were found dead at Kangaroo Lake, near Swan Hill, according to ABC reports.
Professor Richard Kingsford from the School of Biological, Earth and Environmental Sciences at UNSW Sydney said that a combination of local factors and upstream issues contributed to the fish kill at Menindee.
The primary problem for the fish was the lack of oxygen due to microbial activity that depletes oxygen levels in the water.
He said recent flooding allowed a lot of breeding to occur in fish populations. But fish became trapped when the flows stopped coming down the river.
“If we could have got the fish to move a bit more [downstream], that would have helped quite a bit,” Professor Kingsford told The New Daily.
As well as local conditions, Professor Kingsford said climate change exacerbated the problem of mass kills.
Increased temperatures caused bacteria and other microbes to flourish, and that contributed to oxygen depletion in the water, he said.
Dr Paul Sinclair, campaign director at the Australian Conservation Foundation, told TND that barriers within the river systems also contributed to fish kills.
He said that concrete barriers in the river systems make it difficult for fish to move from areas with reduced oxygen to healthier regions.
To address these issues experts suggest:
- Ensuring enough water in the river system for the species that depend on it
- Removing concrete barriers to facilitate fish movement
- Reconnecting floodplains to the river systems, and reconsidering floodplain land use.
‘Too much water siphoned off’
Professor Kingsford said effective management of water resources, particularly tributary systems of the Darling River, was important.
In a recent article published in The Conversation, he wrote:
“Too much water is being siphoned off for agriculture.
“…before news of the fish kills at Menindee, water allocations in the Namoi and Gwydir Rivers were a staggering 113 per cent and 275 per cent respectively. That is to say, all the water farmers and other users could take from these rivers is well beyond the total flows left in the rivers.
“The fish kills at Menindee are the clearest sign yet of how policy and management have failed the Darling.”
Dr Sinclair agreed that mass-scale fish kills were evidence of policy failures by governments.
“Having millions of fish die in the way that they are is telling us that there is something wrong with the management of the river system.
“There is unfinished business in the Murray Darling Basin, in terms of protecting the river system and the life that depends on it.”
Both Professor Kingsford and Dr Sinclair stressed the importance of proper river management and the need for stronger national environmental laws.
A blow to First Nations’ communities
As well as the ecological consequences, fish kills have a significant impact on First Nations communities.
“This must be an incredibly difficult time for First Nations people along the Darling River system in particular,” Dr Sinclair said.
“There’s a number of native species that are being killed that are family totems for First Nations people along the river.”
Professor Kingsford said Indigenous communities should be consulted in future discussions about water management.
“Smaller communities don’t have much of a voice in these discussions, particularly First Nations people.
“I think they should have more voices in the discussions about the rivers and their future. It tends to be dominated by … farming industry groups, which I think [is a] mistake.”
