Flooding rains, ocean gains: how a huge Murray flood gave the sea a feast

by bpckle | Jun 26, 2026 | In the Media

For decades, the rivers of the Murray-Darling Basin have been heavily regulated by dams and irrigation networks. As a result, the volume of water entering the ocean is about 60% smaller than 100 years ago. But nature broke through during massive floods over the summer of 2022–23, when heavy rains filled the Basin’s waterways.

The threshold for a flood on the Murray is when the daily water flow at the Victoria-South Australian border reaches 50 gigalitres a day. This flood reached 168 gigalitres a day – the largest in 66 years. A colossal plume of muddy floodwater reached 40 kilometres out from the Murray mouth into the Southern Indian Ocean.

For marine creatures, this was a dramatic event. What did it do to their ecosystems? To find out, we compared marine animals living directly inside the flood plume with those living further away in normal saltwater.

Our new research found the flood delivered a burst of nutrients into the ocean. We estimate more than 200,000 tonnes of organic carbon were carried out to sea between July 2022 to June 2023 – 29 times more than the same period in 2020–21.

This organic carbon came from the Basin’s rivers and their floodplains, and included large numbers of common carp. Millions of juvenile carp — a highly destructive, invasive freshwater fish — were flushed into the open sea.

Because carp cannot survive in saltwater, they perished en masse. Dead carp piled up on local beaches at astonishing densities of up to 7 kilograms per square metre. In marine rock pools more than 20km from the river mouth, we saw the local crab species such as the purple mottled shore crab and the reef crab having a field day.

How the river fed the sea

These nutrients from the Murray provided a substantial boost to the middle of the ocean food chain. Scavengers such as crabs, and smaller fish such as yellow-eye mullet, were the main beneficiaries. They were feeding on scraps of organic matter, including dead carp, washed in from the Murray River.

We estimate a whopping 35% of the tissues of these animals came from the organic matter carried by the flood in the months afterwards.

Australasian snapper also benefited. These slow-growing larger fish frequently swam in and out of the flood zones. They preyed on smaller fish and crustaceans that had been eating food rich in nutrients from the flood. This means the floodwaters gave snapper and other predators a longer-term boost, effectively storing more of the land and river nutrients in the ocean food web.

How to trace nutrients from a flood

It’s not easy to trace what happens to nutrients from a river once they wash into the ocean. But it can be done.

Every environment has a unique chemical fingerprint, which is reflected inside the tissues of its animals. When nutrients from rivers arrive, they impart part of this fingerprint to the residents of the ocean who eat them – you are what you eat.

We can detect this by testing the muscles of marine animals for these fingerprints.

Ocean water has a uniform sulfur signature. But the crabs we caught inside the flood plume had a very different sulfur signature, which meant they were eating land and river-based food (the carp).

Crabs usually scavenge detritus without much food value. But the crabs inside the flood plume had a heavily enriched nitrogen signature – another sign they had switched to eating dead carp. The crabs had effectively been bumped up a level on the food chain.

Did the nutrient pulse fuel the algal bloom?

In March 2025, a large and long-lasting harmful algal bloom developed off the coast of South Australia. The bloom killed many different marine species in large numbers.

Could the nutrient pulse from floodwaters have fuelled it? The bloom has been linked to a marine heatwave and nutrient-rich seasonal upwelling currents. The 2022–23 Murray River floods have also been proposed as a potential contributor. But this connection remains speculative because of the lag time of 18–24 months and a lack of continuous data collection.

Better monitoring after floods would help us understand whether there is a link.

Rivers matter to the sea

We can see floods not as a waste of water, but as a restoration of longstanding connections between ecosystems disrupted by human control of the river. Our research shows the benefits of these flood events aren’t restricted to land and river ecosystems – they give a major boost to surrounding oceans as well.

Floods are important for the long-term health and resilience of our coastal ecosystems and fisheries, though more research is necessary to fully understand these connections.

Paul McInerney receives funding from the Commonwealth Environmental Water Holder, the Murray Darling Basin Authority and the Goyder Institute for Water Research.

Brenton Zampatti receives funding from the Commonwealth Environmental Water Holder, the Murray Darling Basin Authority and the Goyder Institute for Water Research.

Darren Giling receives funding from the Commonwealth Environmental Water Holder and the Murray Darling Basin Authority and the Goyder Institute for Water Research.

Bird flu is deadly for backyard chickens – and even cats. A vet expert explains

by bpckle | Jun 25, 2026 | In the Media

The deadly H5N1 strain of bird flu has been found in seabirds in two Australian states.

But don’t be fooled by the name: this virus also rapidly infects other animals. It has caused havoc in poultry farms and backyard chicken flocks in the northern hemisphere. And it can also infect, and even kill, cats.

Domestic pet owners, particularly homes that keep backyard chicken flocks, should be on alert for signs of this highly infectious virus. Now is the time to think about how you will respond.

A deadly strain of the virus

I have been working on the H5N1 since 2004. In more than two decades it has evolved into a highly infectious “zoonotic” disease – able to jump between several animal species and occasionally to humans.

The tipping point occurred in the United States in 2023–24, when the virus was transmitted from wild birds into poultry farms and high-density dairy farms in Texas, Kansas, Michigan and Idaho. Transmission has also occurred between cattle and cats, with cats feeding on infected cow colostrum (the first milk after a mammal gives birth), and some later dying.

In the past three years, we have seen many cases in Peru, Chile and southern Antarctica, including the deaths of thousands of seal pups on Heard Island.

How long has it been here?

Initially, Australian authorities were concerned the virus would come predominantly from the north during the annual migration of migratory shorebirds. There was uncertainty about whether sick birds would be strong enough to fly here from far-off Antarctica.

But two of the sick birds in Western Australia and South Australia were found alive. Given this virus was first identified on June 20, it’s possible it arrived in Australia much earlier since these species tend to make their way from the sub-Antarctic region from March onwards.

It makes sense this virus has arrived in winter – it is most easily transmitted during cold weather. In China we saw it typically emerge around Chinese New Year – a time when low temperatures coincide with high demand for poultry for celebratory meals.

How quickly can it move from wild birds?

The World Organisation for Animal Health tracks where the virus is reported for different countries (WAHIS).

Analysing this data, we find it takes between 2 and 6 weeks, on average, for the virus to move into poultry species following the first report in wild birds. Of course, this differs according to the comprehensiveness of a country’s surveillance and the level of data aggregation provided by different countries reporting to the system.

For example, considering data reported between 2020 and 2024 in Denmark, it took a little more than three weeks between finding the virus in wild birds and reporting it in poultry.

In Australia, and considering data from other countries it is possible we will see outbreaks in poultry in the next 4–5 weeks. This obviously depends on the role bridging species will play on bringing infection into Australian poultry facilities, as well as the level of biosecurity of Australian poultry husbandry systems. Everyone is on high alert, and state and federal agriculture departments have ramped up surveillance and public messaging for producers and the public.

In the past few years, an avian influenza surveillance system has tested the faeces of wild birds at nesting sites to watch for the virus. Now this surveillance is likely to be expanded to include poultry. Testing will also be informed by farmers, producers and backyard chicken owners reporting suspected illness.

What’s the risk to my household pets?

Poultry

The risks are very real. When this virus ends up in a densely housed commercial farm, mortality rates of close to 100% are likely. The greatest risk of exposure is when free-range hens spend some time outdoors and are exposed to contact with wild birds. This is the same for backyard chickens.

If you have a flock of chickens, keep them housed as much as possible. “Bridging species” like crows, magpies and other urban birds can bring infection into backyard flocks.

Keep an eye on your chooks and monitor their health for lethargy and neurological signs. If you notice a bird seems disoriented or unwell you should call the Emergency Animal Disease Hotline on 1800 675 888.

If warranted, a biosecurity officer will come and take nasal swabs and bird droppings away to be tested. In the meantime, you will be asked not to move your poultry and to keep them housed.

Unfortunately, all poultry in a farm or backyard flock where H5N1 infection is identified will have to be euthanised.

This virus can infect humans, though it is rare. Do not approach the bird or animal, just call the hotline on 1800 675 888. If there is a need to move the animal, wear gloves and a PPE mask, and dispose of them carefully afterwards.

Cats

Evidence from the US suggests cats are at much greater risk of severe disease than dogs. Where cats ingested contaminated material, such as milk from cattle, there were fatalities. Australian cat owners should be vigilant about what their cat is “investigating” outside, including dead birds.

Dogs

The evidence for serious illness is not as strong as cats. We know they can be exposed, but they don’t seem to be an at-risk species. Other terrestrial carnivores, such as skunk and foxes, have shown neurological illness and respiratory distress. We will have to watch the dingo population closely, because they scavenge on dead wild birds.

Caged birds

Caged birds such as budgerigars are unlikely to come into contact with wild birds. But if this is possible, and there are signs of illness, these should be reported.

Emergency Animal Disease Hotline – 1800 675 888

Ricardo J. Soares Magalhaes receives funding from Australian Research Council.