Up to 300 fish have died in a fish kill event in the Tweed River near Murwillumbah.
Up to 300 fish have died in a fish kill event in the Tweed River near Murwillumbah.

Hundreds of dead fish found on water’s surface

HUNDREDS of dead fish have been found floating in the Tweed River just days after the region was drenched by more than 200mm of rain.

An inspection by Tweed Shire Council officers revealed dead fish on the water’s surface between Condong and the Commercial Rd boat ramp in Murwillumbah.

Waterways program leader Tom Alleston said about 200 to 300 fish were found dead caused by run-off from floodplains.

“Preliminary water quality testing by Council has shown that dissolved oxygen levels and pH is low in the river,” Mr Alletson said.

“We believe that run-off from floodplain areas affected by acid sulfate soil is the most likely cause of the fish kill.”

Council has been removing fish affected by the fish kill from the river.
Council has been removing fish affected by the fish kill from the river.

Mr Alleston said acid sulfate soil was a naturally occurring type of soil found extensively in low lying areas of the Tweed River floodplain, and across vast areas of the east coast of Australia.

“When exposed to oxygen, the mineral pyrite which is found in these soils reacts to form sulfuric acid,” he said.

“After periods of prolonged drought when the groundwater table is low and acid sulfate soils become exposed to the air, more acid is formed.

“When a large downpour flushes this acid into the river, it is common for fish kills to occur.”

He said council had been removing the dead fish and would continue to monitor floodplain drains where poor quality water was entering the estuary.

“It is possible that the quality of water flowing off the flood plain could get worse in coming days,” Mr Alletson said.

“How this may affect fish and other aquatic life cannot be predicted at this time, however it is likely there will be some dead fish within the river for days to come.”



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