EXPERT REACTION: What killed a million Darling River fish?
It has been reported that a million fish have died along the Darling River. Officials initially blamed drought and rapid shifts in water temperature disrupting algal blooms. Locals, however, aren't convinced, saying the issue stems from the State and Federal Government's poor water management and irrigation farming.
Organisation/s: University of Technology Sydney (UTS), The Australian National University, Charles Sturt University, The University of Queensland, University of South Australia, The University of Adelaide
These comments have been collated by the Science Media Centre to provide a variety of expert perspectives on this issue. Feel free to use these quotes in your stories. Views expressed are the personal opinions of the experts named. They do not represent the views of the SMC or any other organisation unless specifically stated.
Simon Mitrovic is an Associate Professor in Freshwater Ecology at the University of Technology Sydney
Algal blooms are fairly common during summer in the Lower Darling River when the river is at low flow. It is unusual to get a fish kill occurring at the same time. I suspect that the algal bloom respiring (taking oxygen out of the water at night) combined with the heavy rainfall in mid-December that may have mixed the water column (bringing up low oxygen water from the bottom of the river to the surface) and associated runoff with organic matter going into the river (breaking down and using oxygen) may have brought oxygen levels down low enough to result in the fish kills.
What is Rotten in the Murray-Darling Basin?
Message to our leaders: dead fish and dying rivers are not because of the drought, it’s because we are extracting too much water from our rivers as many of the large fish which are dying have lived for more than 50 years through many equally severe droughts. Drought is part of the system and any plan must be able to manage our rivers through drought whilst maintaining ecological resilience of the rivers and floodplains. Clearly, the current MDB plan has failed to do that. This current tragedy was predicted and is no surprise. The river is like a piggy bank, if you keep taking money out without saving for the future you end up bankrupt, and just when you need it the most. This is about a failure of water reform, and a dereliction of duty to deliver the intention of the Water Act 2007. The drought is simply the straw that broke the camel’s back.
Whilst these large fish kills result ultimately from depletion of oxygen levels in the water, the causes sit clearly with the management of nutrient levels and water flows in the streams, floodplains and billabongs of the river system. It is the management of water extraction in the northern tributaries to the Darling that is a primary determinant of the Darling River flow regime. Some 3,300 GL of water entitlement is allocated to these tributaries, of which some 1,200 GL was extracted for irrigation in 2014-15 following significant inflows to the system in 2011-2013. How the extractions are managed in drought to protect the ecological integrity of the aquatic ecosystems is thus a key question which must be addressed as global warming expresses its footprint into our future. Clearly this has not been done and the fish kills point to our failure with the current implementation of the Basin Plan. The question remains: where has the water gone in the last two years? In the last year, as little as maybe 35GL arrived at Bourke from its tributaries on top of the Darling. At this time of drought, how well was the water used to protect the foundations of the river’s aquatic ecosystems? This is the critical question.
Those in charge who acted against or failed to look after the public good interest, as set out clearly in the Water Act 2007, must be held to account. Australians can do better than this. The vision of returning the Basin Rivers to healthy, sustainable, working rivers has been lost. We must find it again and place it on centre stage. It’s a national shame and international embarrassment how we are currently managing our iconic and much-loved river system.
The algal bloom in the Darling River is devastating for the river ecosystem and local communities. This algal bloom has the potential to spread further downstream, or similar conditions may trigger new outbreaks of algae elsewhere along the river system. In the absence of sufficient water in the Menindee Lakes to flush the system, some local actions can be implemented that could potentially save a small number of fish.
We can draw on the experience of a hypoxic blackwater event in the Murray River in 2016, where a lot of fish died due to low dissolved oxygen (DO) concentrations following a large flood. While this event was not caused by an algal bloom (it was due to high concentrations of dissolved carbon in the water) the outcome of low DO and subsequent fish deaths were similar to what is currently occurring in the Darling River.
In 2016 when it became evident that a hypoxic blackwater event was likely, members of the community in the Edward-Wakool system installed aerators (different shapes and forms, some home-made) to create patches in the river (or ‘refuges’) that had higher DO. Water managers were also able to call on water from nearby irrigation canals to provide environmental flows and create small refuges with higher DO. There is evidence that these actions helped a small number of fish and other aquatic organisms to survive.
Whilst these local actions did not prevent further fish deaths occurring outside the created refuges, the individual fish that did survive will have contributed to the recovery of the river ecosystem in the years following the event. It needs to be understood though, that the lack of water in Menindee Lakes to provide flows will make it more difficult to create small refuges in the case of the Darling River.
During previous hypoxic events, the community felt powerless and were devastated when they observed fish dying. However, during the 2016 hypoxic event, they rallied around and installed these aerators that had the potential to make a small difference. Local actions such as these could be initiated in other parts of the Darling River before the algal bloom spreads further and DO concentrations drop too low. It is essential to initiate actions before the algae bloom spreads to these downstream sites or new outbreaks arise elsewhere.
We have been here before with the algal bloom of 1991 along the Darling River and the 'blame game'. Water reform and the Basin plan was supposed to fix this, but it hasn't.
The problem is that we are extracting too much water from the river and not leaving enough for the fish or anyone else who actually wants to swim or enjoy our river systems.
The NSW Irrigators Council would have us believe it is all about the drought. It isn't. It about taking too much water upstream so there is not enough for downstream users, and the fish.
It's time to make those in charge (elected and appointed) accountable for lowering the volumes needed to increase stream flows, it's time to call out the regulators who have been 'asleep at the wheel' in relation to water theft and managing stream flows.
This is about integrity and it's about the misuse of public money. Billions have been spent on upgrading irrigation infrastructure (with payments, on average, of hundreds of thousands per irrigator) but with no public benefit. It's a disgrace and it's time those responsible are held accountable for this unfolding disaster.
This disaster is sadly unsurprising. The Murray Darling Declaration, released by leading water experts in 2018, pointed out how political decisions driven by ignorance and expediency have compromised the environmental goals of the 2007 Water Act, and led to massive waste of public funds on projects of little or no benefit.
As stated in the Declaration, the following measures are urgently required:
- Stop any further expenditures on infrastructure related to water-use efficiency.
- Audit, through a comprehensive and independent evaluation, the environmental and socio-economic outcomes of water recovery undertaken to date.
- Establish a truly independent and scientifically based entity to publicly document what is happening in the basin and to ensure delivery of the key objects of the Water Act 2007.
Australia needs more national intervention in water governance. We need the Water Act to be applied to the entire nation. There is no reason in law why it could not.
The Water Act could be improved by adding an institution made up of scientists (social and physical scientists) to holistically consider the impacts of water use proposals upstream and downstream. We need to stop the partisan way of approving schemes that only considers local interests.
The purpose of a national scheme would be to air local and regional issues and hence create a transparent process.
Reduction of the risk that this will happen again requires an MDBA [Murray-Darling Basin Authority] decision to
- set minimum daily 'hands off' flow requirements for every river reach, as is done in the UK;
- introduce a 'Darling River rule' from the start of the next irrigation season to limit extraction to those places where off-take is metered: no meter means no water.
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