Bony herrings, golden perch and Murray cod were found washed up on the shores of Lake Wyangan over the weekend.
However, the cause of the large fish death has been established yet.
On Monday, NSW Department of Primary Industries fisheries staff travelled to the lake to assist with investigations.
A NSW DPI spokesman said the fish death "is likely related to water quality issues in the lake".
Griffith City Council's general manager has said it's "too early" to speculate on the cause of the fish deaths.
Council reported the incident to the NSW Environmental Protection Agency and the NSW DPI.
"Council recognises the severity of this situation and has taken prompt action with staff attending Lake Wyangan upon notification of the dead fish washing up on shore," Mr Stonestreet said.
"Samples have been taken of each fish species and will be analysed.
"Several water samples have also been taken and are being sent to an independent laboratory for testing."
Earlier this month, around 240 megalitres of water flowed into the northern lake through southern inlet, with recent rain adding to the total.
Council is developing a tender to construct a series of sedimentation ponds and wetlands at Lake Wyangan to help improve the quality of water entering the lake.
Griffith's Joel Undy said the fish death was disappointing as some of the fish were quite old.
A keen fisherman, Mr Undy has spent many years fishing at Lake Wyangan. He said many fisherman were just getting back into the swing of things.
"When I was a kid we'd catch 30 fish a day in the boat," he said.
Mr Undy said some Murray cod had measured up to a metre long making them around 30 years old.
Griffith Business Chamber's acting president Paul Pierotti described the fish death as a "disaster" for Griffith and said an investigation was critical.
Mr Pierotti said the fish death was the latest crisis in the "long history of lake mismangement".
"This issue has now come to a head and we are calling on the NSW Government to launch an inquiry into the management of Griffith's most cherished natural asset," he said.
In 2018, council resolved to sell some water entitlements bound for the lake in order to create a budget for a long-term solution.
"The facts are now clear, that council's negligent decision to sell water rather than keep Lake Wyangan refilled has contributed to this tragedy," he said.
"Under the management of Griffith City Council, Laker Wyangan has become a dangerous embarrassment rendered useless as a recreational waterway with toxins in the water linked to motor neurone disease."