NSW Fisheries yesterday launched an investigation into the deaths of thousands of fish scattered along the eastern shore of Lake Keepit at the Manilla Ski Gardens.
The cause at this stage is believed to be low oxygen levels but sample testing could prove inconclusive because experts believe the fish have been dead for too long.
Locals and fishermen said reports of the deaths go back to the beginning of the week when scores of carp and bony bream were first observed and hundreds more Murray cod and yellowbelly were found belly-up.
Fish were also seen gasping at the surface and hundreds of shrimp, since cleaned up by local birdlife, were seen climbing out of the water.
Yesterday fishermen were still amazed at the scenes confronting them on the shorelines of the dam.
Some were convinced something fishy was going on, with one theory on how the fish died including poisoning from nearby crop dusters.
The fish deaths occurred along a two kilometre stretch in the upper end of the lake known as “the forest”, which has been inspected by a NSW Department of Primary Industries (DPI) fisheries officer.
The DPI said the kill was first observed on Monday but only reported to the department yesterday.
A DPI spokesman said water above the kill looked dirty compared to downstream and weather conditions prior to the kill were hot and dry.
That was followed by afternoon thunderstorms with about 25 millimetres of rain recorded in the area.
Those factors and a dam increase from 34.5 per cent capacity at the time of the kill, to a current capacity of 40 per cent, are believed to have resulted in low dissolved oxygen levels.
“No water samples have been collected because the delay in reporting the kill means that the results would be inconclusive,” the DPI spokesman said.
He said it proved the importance of reporting fish kills as soon as possible to ensure fish and water quality samples could be obtained close to the time of the incident.
Gunnedah fisherman Trimmer Wicks was convinced the deaths were from poisoning, possibly from nearby crop spraying.
He fishes at the ski gardens spot, south-west of Manilla, regularly and has never seen anything like it before.
He saw hundreds of carp and Murray cod while other fish were still swimming around.
“Carp are tough ... you can cut their heads off and they’ll swim away,” Mr Wicks said.
“If it’s poison, it would’ve had to pack a punch to kill them.”
Mr Wicks said he started to see dead fish on Wednesday evening but there was now hundreds more.
Yesterday morning, he said the fish didn’t yet smell but they were starting to blow up in the hot sun.
Lloyd Gorrie and his partner Julie also fish at the spot frequently and agreed it was definitely out of the ordinary.
A keen fisherman originally from Gulgong, Mr Gorrie said he had fished in the area for the past 15 years and never seen or caught a sick fish.