The death of around 500 bass at Clarrie Hall Dam was a ‘natural event’ according to Tweed Shire Council.
About 500 fish were found dead in the deepest part of the dam, near the spillway on Friday. The fish have been removed and disposed of.
‘Clarrie Hall Dam has undergone a seasonal overturn in the past two weeks, where the deeper de-oxygenated waters have upwelled to the top of the water column,’ the Council’s Acting Manager for Water and Wastewater, Michael Wraight, said.
‘This is a natural process and happens annually around the beginning of winter as the top water layers cool and sink to the bottom forcing the bottom layers up.’
Historically there have been overturn events at Clarrie Hall Dam, which have resulted in similar fish deaths.
Testing of water samples in the dam over the past two weeks shows very low oxygen levels in all levels of the dam near the spillway.
‘It is likely that these low dissolved oxygen levels have resulted in the death of the fish. We don’t expect it to get any worse but will continue to monitor the situation,’ Mr Wraight said.
New South Wales Fisheries has been advised of the fish kill.