Thousands of Fish Found Dead in Western NSW Lake

Fisheries staff inspected the lake on July 8 and attributed the deaths to a ‘winter die-off,’ triggered by sudden drops in water temperature.

A supplied image obtained on March 17, 2023, of thousands of dead fish that have washed up at the main weir at the Menindee Lakes, in outback NSW, Australia on March 16, 2023. AAP Image/Supplied by Geoffrey Looney

Thousands of fish have been found dead along the banks of Lake Cargelligo in western New South Wales (NSW), sparking a formal investigation by the state’s fisheries department.

The mass fish kill event—centred around the town located 200 kilometres west of Parkes—has raised alarm among ecologists and locals alike.

The NSW Department of Primary Industries and Regional Development (DPIRD) has confirmed the mass die-off, estimating that thousands of bony herring, also known as bony bream, have been affected.

Fisheries staff visited the lake on July 8 and said the deaths are likely due to a “winter die-off,” a phenomenon where plummeting water temperatures severely stress the fish.

“Bony herring can become stressed or die when water temperatures drop,” DPIRD told The Epoch Times, noting this species is particularly vulnerable to such conditions.

Fish Deaths Escalate After Initial Signs

Aquatic ecologist Adam Kerezsy was the first to notice a handful of dead fish at both Lake Cargelligo and nearby Lake Curlew about two weeks ago.

Since then, the number has grown exponentially, with silver-scaled carcasses now lining the lakeshore in the thousands.

Fish kills are sudden, large-scale die-offs and can occur at any time of the year, though they are more common during periods of extreme weather. Cold snaps and sudden changes in water temperature are well-documented triggers—especially for temperature-sensitive native species.

The incident appears to be limited to bony herring, a key component of the local ecosystem and a food source for species such as Murray cod, golden perch, and various water birds.

Fish Kills Not New to Region

DPIRD website details that this is not the first such occurrence. Last winter, a similar fish kill in the region involved a range of species, including small Murray cod and threatened freshwater catfish.

In another incident in July 2024, up to 50 dead bony herring were reported in the Murrumbidgee River near Hay.

In February, thousands of dead fish—including Murray cod, golden perch, freshwater catfish, bony herring and carp—were reported near the junction of the Peel and Namoi rivers. The NSW Department of Primary Industries attributed that incident to poor water quality and low dissolved oxygen levels, following a period of heavy rainfall and runoff from nearby creeks.

Authorities are urging residents to report any further fish deaths or unusual aquatic activity to the Fishers Watch hotline at 1800 043 536.

DPIRD said it is taking the matter “extremely seriously” and will continue monitoring the situation closely to assess any further risks to the lake’s biodiversity.