Collie River dead fish: Hundreds of rotting fish carcasses found on river banks as authorities investigate

Craig Duncan
The Nightly
2 Min Read
Up to 700 fish have washed up dead along the banks of the Collie River in Australind
Up to 700 fish have washed up dead along the banks of the Collie River in Australind Credit: Craig Duncan

The picturesque banks of the Collie River, in WA’s South West, have been somewhat spoiled lately by the stench of something fishy.

The bloated bodies of black bream and mullet can be found along the length of the river as about 700 fish are estimated to have died along the waterway.

A Department of Water and Environmental Regulation spokesperson said they had received reports of the fish kill event stretching from the Lower Collie River between the Australind Bypass bridge and Eaton Drive bridge.

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DWER staff have taken samples from the site and will be putting up signage to warn the public to avoid the area as a precautionary measure.

South West NRM sustainability and environment lead Linda Metz said it was difficult to know what caused these fish kills without testing, however the likelihood of these events was known to increase after periods of heavy rainfall.

“Increased rainfall creates an associated increase in nutrient runoff into our water systems which promotes elevated levels of a naturally occurring algal bloom and is potentially toxic to fish,” she said.

The DWER spokesperson said preliminary results indicated the fish kill was likely due to very low dissolved oxygen through the area.

“The flows associated with rainfall at this time of year can wash in nutrients and organic matter, mobilise nutrients in sediments, and mix the water, bringing low oxygen conditions to the surface,” they said.

“As this was the first significant rainfall since October 2023, with heavy rains falling in a very short period, a large amount of nutrients and organic matter entered the Collie River in a short space of time.”

Hundreds of fish have washed up dead along the banks of the Collie River in Australind.
Hundreds of fish have washed up dead along the banks of the Collie River in Australind. Credit: Craig Duncan

The spokesperson said the sudden influx of freshwater into the system also could lead to algae blooms, which would have contributed to the death toll.

One local fisher said this was the third time he had encountered fish kills along this section of the Collie River.

He said incidents like this made him concerned for the future of fish stocks in the waterway.

Community members who encounter high numbers of dead fish are encouraged to report their discovery to the FishWatch Hotline on 1800 815 507.

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