NSW Department of Primary Industries inspectors, praised for their rapid response to thousands of fish killed on Lake Cargelligo last week, have confirmed the reasons for the deaths in a statement to the Western Plains App.

''NSW Department of Primary Industries and Regional Development (DPIRD) Fisheries is aware of a fish kill affecting Bony Herring at Lake Cargelligo last week.

"DPIRD Fisheries staff attended the site on 8 July in line with the fish kill protocol and estimated that thousands of Bony Herring have been affected.

"Bony Herring can become stressed or die when water temperatures drop – this is known as ‘winter die off’.

"DPIRD Fisheries staff have confirmed that this is the suspected cause of this fish kill event."

Reacting to the Department's statement, local resident and aquatic ecologist Adam Kerezsy said ''There is no real surprise (about their findings) but when lake levels were lowered to 50 per cent it also effected the tiny native species of 10-20cm.''

In June this year, WaterNSW began lowering Lake Cargelligo to 50 per cent capacity for the next phase of a major embankment upgrade project that began in 2023.

WaterNSW said at the time they would continue to supply stock and domestic replenishment flows from Lake Cargelligo.

Water levels were gradually reduced to 50 per cent and are expected to be maintained at 50 per cent until the end of September 2025. 

Any excess flow above downstream demand will be captured in nearby Lake Brewster to minimise water loss.

Dr Kerezsy who lives by the Lake said he will continue to do some further personal research on the fish kill.

Barwon MP Roy Butler visited the Lake on July 8 and Water NSW and Department of Primary Industries inspectors took samples of water.

WaterNSW encourages community members to report any further fish deaths or observations through the Fishers Watch hotline on 1800 043 536.

For more information on fish kills, visit their website.