Local fisherman and residents reported the incident on Thursday, after a small number of Murray Cod and Golden Perch, along with hundreds of carp and thousands of bony brim were found along a two kilometre stretch of the dam. 

Hundreds of shrimp were also spotted.

Gunnedah fisherman Alan Wicks was out on the water last Wednesday when he found the dead fish. 

A keen angler, he said there were at least nine Murray Cod up to 40 pound in weight that were dead.

“It was shocking,” he said. 

“They were all dead and had started to bloat up on the edge of the bank everywhere. There were a few floating around in the water.”

The incident was reported to the Department of Primary Industries (DPI) and a fisheries officer was sent to inspect the kill.

A spokesperson for the DPI said the deaths appear to have occurred some time ago and therefore any water samples taken would mean the results would be inconclusive. 

The suspected cause, however is dissolved oxygen levels, which is associated with hot and dry weather, coupled with high rainfall. 

It’s understood fish kills caused by low oxygen levels is common in the summer months. 

“Weather conditions prior to the kill were hot and dry, followed by afternoon thunderstorms with approximately 25mm of rain recorded in the area,” the DPI spokesperson said.

The dam at the time of the kill was down to 34.5 per cent capacity, but has since had about 4000ML of inflow, bringing the capacity up to approximately 35.5 per cent. 

The DPI says it is monitoring the situation and asking the public to report any further sightings of dead fish as soon as possible to the Fishers Watch hotline on 1800 043 536.

Immediate reporting is necessary to ensure that fish and water quality samples can be obtained as close to the time of the incident as possible.