A million dead fish & maladministration: could the Murray Darling fish kills really have been prevented?


Retching? Crying? You should be doing both (Source: The Guardian, 2019)

Death of a 100 year old Cod

It’s been over a month since the first large scale death of fish at the now unfortunately well-known town of Menindee, located within the lower Murray-Darling river system. This was tragically followed by two more mass fish deaths, ‘only’ occurring in the thousands after the initial death of an estimated one million vulnerable Murray Cod, Golden perch, bream, and other native fish species.

For those non-fishers out there, the Murray cod (Maccullochella peelii) is the largest native Australian freshwater fish species, and probably the most iconic. They are particularly impressive as they can live for more than 50 years (even up to 100 years, as shown in the clip that went viral below), have been recorded weighing over 100kg, and can move hundreds of kilometres. It is important culturally and as food for Aboriginal people, and also remains one of the most popular recreational fisheries in Australia.

On top of that, previous research has found much of the Murray Darling Basin’s native fish population comes from the Menindee Lakes and lower Darling River, with these waterways critical for fish breeding, making these mass deaths all the more of an ecological disaster.

And to make matters worse, it seems that the “disgusting mud-sucking ” and invasive Carp (thanks Barnaby) have survived it all due to their ability to deal with extreme temperatures, poor water quality, low oxygen environments (some have even been observed going above water for air).

Why did it happen?

Many farmers, fishers, members of the general public (and indeed politicians for the obvious reasons) are now, unsurprisingly asking why this happened. And more importantly, could these mass deaths have realistically been prevented?

Investigations are now underway and the likely answers as to why the mass deaths occurred are (of course) not simple. It’s well known that low/no oxygen means suffocating fish in any waterway. But why were oxygen levels in the lakes and river being depleted?

The key reason presented by CSIRO and others has been the growth of a big blue-green algal bloom, which are known to suck out oxygen from waterways as they decompose. It should be stated that algal blooms do occur naturally but do not usually cause the scale of fish deaths recently seen. To grow, algal blooms need:

  • warm weather;
  • stagnant water;
  • direct sunlight (irradiance, a lack of cloud cover); and
  • high nutrient levels.

Fish deaths are usually minimised when this happens if they have somewhere safe to escape the bloom and low-oxygen conditions (these can be both natural or artificial refuges).

So why did fish deaths occur at Menindee in such huge numbers? The CSIRO proposes that it was because of a combination of factors including:

  1. Drought conditions leading to stagnant water in the region, which has received less rain than ever before in some parts;
  2. Development of an extensive and concentrated blue-green algal bloom due to a heatwave, no water flow, and high nutrient levels;
  3. Sudden drop in temperature as the results of a passing cold front, leading to  mixing in the water column bringing up anoxic (deoxygenated) water; and
  4. The fish had no refuge to swim to because the entire water column (from river surface to riverbed) experienced low oxygen levels, resulting in their death.

A natural query that many people have since had is: if there was more water flowing down the river then could this have been prevented?

This is a bit of a loaded question because a significant volume of water in the Murray Darling has been allocated to irrigators as defined by the Murray Darling Basin Plan, and as a result, irrigators and regulators both (i.e. Murray Darling Basin Authority and the NSW government) have been the target of significant animosity.


Boundary of the Murray Darling Basin Plan. Menindee is located in the southern basin near Broken Hill, ~200 km upstream of the Darling River’s junction with the River Murray.

The Murray Darling Basin Plan

The Murray Darling Basin Plan outlines water allocations between the environment, farmers, communities, and industry, essentially defining how much water can be diverted or flow down the river system. It was signed by federal and state governments in 2012, with a commitment to return at least 2750 gigalitres of water to the river. However, the agreement fell short of scientific recommendations that at least 4000 gigalitres of water must be returned to ensure the river’s long-term survival.

At the moment the river system and associated water storages are running at about 35%. In times of drought the Murray Darling Basin Plan prioritises water allocations for critical human needs (i.e. drinking and household water), however, all allocations are reduced, regardless of whether the water is for farming or for the environment.

In 2015 federal legislation was introduced which caps the amount of the water that can be “bought back” for the environment, with the intent of providing certainty with respect to water access for local industry and communities. However, moves are now being made by political parties to lift this cap in order to allow more water to be returned to the environment in response to the drought and fish deaths, which is unsurprisingly creating turmoil for those in the regional areas such as the Goulburn Murray irrigation district who would be affected by this.

While the NSW government has previously installed aerators in an attempt to increase the amount of oxygen in parts of the river system as small refuges for fish, the latest fish kills occurred upstream from these aerators. A plan to install more solar-powered aerators is also on the cards, however, will only work as a stop-gap measure.

Blame game & maladministration

Until the ABC’s 4 Corners program in July last year, many Australians were unaware of alleged water theft and grossly deficient compliance along the Darling River. Most locals believe the fish kills are the direct result of the government’s decision to empty the Menindee Lakes in 2016 and 2017 and send the water downstream to other storages, leaving almost no water for flows during the prolonged drought suffered by the region.


While State NSW and Federal government representatives have attributed the fish deaths to the extreme drought that the region is suffering, and the sudden drop in temperatures resulting in low oxygen levels described earlier, poor management is now a likely factor. Findings from the SA royal commission on the Murray Darling Basin Plan include gross maladministration, negligence and unlawful actions.

The report found the original plan ignored potentially “catastrophic” risks of climate change. In addition, while the NSW Water Act requires environmental priorities to be given primacy when determining an ESTL (the amount of water which can safely be taken from the river), it was found that the State government had adopted a “triple bottom line” approach, where it considered economic and social factors to reduce the recovery target for the environment. The report recommended major reform, including resetting water-saving limits, and dumping major projects such as the Menindee Lakes project proposed by NSW.

So was it preventable?

It is known that algal growth can be suppressed when flows increase above a certain threshold. While this works well under “normal” conditions, it may be difficult to prevent algal growth during a drought, especially when a river is separated into stagnant pools.

However, increased river regulation and restricted flows over past decades have seen the number of algal blooms increase in the Murray-Darling Basin.  Numerous experts have called the fish deaths a preventable catastrophe.

A number of Australian professors have come together stating that the recent fish deaths were entirely predictable (e.g. ecologists investigating the 2004 fish kills in the lower Darling recommending improving water quality by increasing adequate storage levels ifto prevent such events from happening again), with some 1,200 billion litres of water extracted for irrigation in 2014-15 in the Northern Basin yet only a tiny fraction, (~35 billion litres), actually arriving from upstream in the past year.  They also propose immediate action, saying too much water is being removed from the northern Basin and irrigators need to reduce their take to correct the flow regime and prevent further fish deaths in the future. Experts are also calling for the establishment of an independent expert scientific advisory body to monitor the basin’s health and to publicly guide all governments to ensure the full achievement of key objectives of the Water Act 2007. i.e. to restore over-allocated resources to environmentally sustainable levels of extraction; and to protect, restore and provide for the ecological values and ecosystem services of the Murray-Darling Basin.

On the basis of expert opinion in conservation biology, ecology, water policy and economics, it appears that it is safe to say that mismanagement in combination with drought and climate change were the cause of the large scale fish deaths. And given that we have the science to understand how climate change and riverine ecology and hydrology relate, it is likely that these events were largely preventable if greater flows were allowed to flush the system.

Difficult decisions

According to the Parliamentary Library, the majority of the water used from the Murray-Darling Basin is employed in agriculture. In 2005-2006, cotton farming accounted for 20 per cent of that amount. The NSW Irrigator Council has said that reductions in water uptake for NSW irrigators would “destroy” the cotton industry and their associated communities. And it seems like a terrible irony that while drought is occurring across far west NSW, flood waters are overwhelming the people of Northern Queensland at the huge cost of livestock and livelihoods.

The unfortunate and difficult decision both government, the local community and general public need to make is what do we prioritise: a healthy functioning river system that can survive extreme events and support its multiple habitats and wildlife, and also provide the significant social, cultural, and environmental values for both the Aboriginal Barkandji people of western NSW, recreational fishers and wider Australian community; or do we prioritise the continuing of the cotton and other water-intensive agriculture and their regional communities? Because at the moment we are locked in a stale mate and it seems we can’t have both.

And if the tears and retching of grown men, crying over 100 year old fish, don’t move you to make a decision on this issue, well then you have a hardened heart indeed.