For many Tasmanians, the River Derwent is more than just a waterway—it’s a place for family picnics, fishing trips, and peaceful strolls along the shore.
But over the weekend, locals were met with a distressing sight: hundreds, possibly thousands, of small dead fish washed up along the riverbanks between Crayfish Point in Taroona and Long Beach in Sandy Bay.
The discovery has left the community rattled and raised serious questions about the health of one of Hobart’s most beloved natural assets.
A disturbing trend emerges
Social media quickly filled with photos and worried posts from residents, many of whom described the scene as ‘disturbing’ and ‘heartbreaking’.
The dead fish, believed to be pilchards or sardines, were scattered along the water’s edge and beaches, creating a grim spectacle and a foul odour that lingered in the air.
This isn’t the first time Australians have witnessed such events. In recent months, mass fish deaths have been reported up and down the east coast, from New South Wales to South Australia.
In March 2025, thousands of juvenile leatherjacket fish washed up on beaches stretching over 300 kilometres from Stanwell Park to Bermagui.
South East Queensland and South Australia have also seen similar incidents, with environmental factors and disease outbreaks often to blame.
What’s causing the fish deaths?
Authorities launched an investigation immediately. Biosecurity Tasmania and the Environment Protection Authority (EPA) collected samples from the affected areas.
Early test results have ruled out some of the usual suspects, such as Tasmanian rickettsia-like organism (TRLO) and P. salmonis, both of which are known to cause disease in farmed salmon.
However, some samples have tested positive for pilchard orthomyxovirus (POMV), a virus from the same family as influenza—but don’t worry, it only affects aquatic species. Atlantic salmon and Australian pilchards are particularly vulnerable.
While POMV is often present in the environment without causing major issues, outbreaks can occur when fish are stressed by factors such as:
- Warmer water temperatures
- Low oxygen levels
- Pollution or poor water quality
- Handling or overcrowding
When these stressors combine, the virus can spread rapidly, leading to symptoms like lethargy, erratic swimming, loss of appetite, and, in severe cases, mass die-offs.
Environmental factors at play
It’s not just viruses that are causing concern. Environmental scientists point to a range of factors that can contribute to fish kills, including:
- Sudden changes in water temperature (often linked to climate change)
- Algal blooms, which can deplete oxygen and release toxins
- Pollution from urban runoff, agriculture, or industry
- Natural events like storms or cyclones, which can stir up sediments and disrupt ecosystems
In South Australia, for example, a toxic algae outbreak recently killed fish, octopuses, and cockles (pipis).
Earlier this year, in Tasmania, a major crisis unfolded when over 5,500 tonnes of farmed salmon died due to a bacterial infection.
The decomposing fish and oily waste washed up on beaches and caused a public outcry.
The bigger picture: Is this the new normal?
While the current fish kill in the Derwent appears to be localised, it’s part of a worrying pattern. As our climate warms and human activity continues to put pressure on waterways, these events may become more frequent.
The changes are particularly stark for older Australians who have watched the Derwent’s ebb and flow for decades.
The recent salmon farm die-off in Tasmania has also reignited debate about the sustainability of aquaculture in the state.
Many locals are calling for greater transparency and stricter oversight of fish farming operations, which are often blamed for contributing to water quality issues and disease outbreaks.
What’s being done?
Authorities are continuing to monitor the situation closely. Further testing is underway to determine if other factors are at play, and officials are monitoring nearby marine environments to assess any broader impacts.
The EPA and Biosecurity Tasmania have assured the public that they are taking the matter seriously and will provide updates as more information becomes available.
In the meantime, environmental groups are urging the community to report any further fish deaths or unusual activity along the river. If you’re out for a walk and notice something amiss, don’t hesitate to contact local authorities.
How can we help protect our waterways?
While some causes of fish kills are beyond our immediate control, there are steps we can all take to help protect our rivers and oceans:
- Dispose of chemicals, oils, and rubbish responsibly—never down the drain or into waterways
- Support sustainable seafood choices and responsible aquaculture
- Get involved in local clean-up days or river care groups
- Advocate for stronger environmental protections and monitoring
Have you noticed changes in your local waterways?
We’d love to hear from you. Have you witnessed similar events in your area? Do you have memories of the Derwent or other rivers from years gone by? Share your stories and thoughts in the comments below—your voice matters in the conversation about the future of Australia’s precious waterways.
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