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Australia's catastrophic fish die-off: What has happened since 2019

As this summer draws to a close, it marks just over a year since successive fish death events at Menindee in Lower Darling River made global headlines.

Two independent found high levels of blue-green algae and low oxygen levels in the water caused the deaths. Basically, the fish suffocated.

The conditions were caused by a combination of water extraction and extremely dry conditions which effectively stopped the river from flowing. Both investigations concluded that until more water flowed in the Darling, in western New South Wales, further fish kills were very likely.

So what's happened since, and does the recent rain mean the crisis won't be repeated?

Federal and state government action

In April last year the to improve the river's health and prevent more fish deaths. Let's examine what's been done so far:

• Native fish management and recovery strategy: Parts of a draft native fish management and recovery strategy have been released for . The plan has included governments, academics, the community and indigenous groups.
• Native fish hatchery: Government to hold and breed more fish. But reintroducing fish into affected areas is challenging and could be a decades-long program.
• Research: The government committed to . A panel has been and the oversight committee is scoping the most effective research outcomes to better manage water under a changed climate.
• Fish passage infrastructure: Fish ladders—structures that allow fish to travel around obstacles on a river—are needed at sites on the lower and upper Darling. Fish ladder concept designs have progressed and are also part of the .
• In-stream cameras: Live-stream feeds of the Darling River are not yet available.
• Meter upgrades and water buybacks: and return water to the rivers. Rollout of improved metering is due .

Progress on these actions is welcome. But the investigation panels also recommended other actions to help fish populations recover over the long term, including ensuring fish habitat and good water quality.

Further fish deaths

In 2003, basin native fish communities were estimated to be at and the spates of fish deaths will have reduced this further.

Over spring and summer in 2019, conditions in the Darling River deteriorated. A series of smaller, but significant, fish deaths prompted . Aerators were deployed in a bid to improve the de-oxygenation. Fish were moved to more suitable water bodies, or to hatcheries to create insurance populations.

By spring, once-mighty rivers such as the Darling and had dried to shallow pools. As summer progressed, more than 30 fish die-offs occurred in the .

What about the rain?

Strong recent rainfall means upper parts of the Darling catchment are now flowing for the . Flows are passing over the .

A flowing Darling is great, but it raises questions over future water management. Farmers have been waiting for years for the Darling to flow and will be eager to extract water for agricultural productivity. Likewise, the environment has been awaiting a "flush" to reset the system and restore ecological productivity.

After the rains, the NSW government to harvest floodwaters to reduce the threat of damage to private infrastructure. Now that threat has subsided, governments are working together to "actively manage" the event—meaning water rules will be decided as the flow progresses, in consultation with water users and environmental managers.

But there is still

Is a flowing Darling a return to normal?

The current flows in the Darling are far from a return to normal conditions. NSW is still in drought, and the river flows are yet to reach the Lower Darling. Many have not seen a flowing Darling in their lifetime.

Indigenous elders and recreational fishers—those who remember – are lamenting the recent declines. In parts of the system, dry riverbeds and isolated pools are still begging to be connected so fish can move about, spawn, and naturally recover.

River flows could take up to six weeks to reach the lower Darling, and follow-up rain is urgently needed to avoid another summer of fish carnage. Future water sharing strategies must protect both upstream and downstream communities. Some people are lobbying for the Menindee lakes to be to ensure biodiversity and water management work together.

Undoing over 200 years of fish declines will require a sustained effort, with a significant investment in recovery actions over a long period. We must recognise Australia is a country of long droughts and flooding rains, and develop a proactive native fish strategy that reduces the probability of a similar disaster in future.

But unfortunately, as history has shown that when we transition from drought to flood, .