Residents noticed the stingrays dying in the waterway three weeks ago and contacted NSW Fisheries.

Lake Conjola and Districts Lakecare spokesperson Robin Kerves said nothing had been done to help more than 36 rays that had died near the lake entrance.

She claimed the animals were dying because the lake was closed and they could not get out to the ocean, which was up to 10 degrees warmer.

“They are lining up and obviously attempting to get out of the lake,” she said.

“The lake has dropped to seven degrees compared to the ocean temperature that is around 16 or 17 degrees.”

On Thursday morning 38 rays, up to 50 centimetres in size, were dead near the Cunjurong Point boat ramp and many more were swarming towards the closed entrance.

Mrs Kerves claimed Fisheries was “ignoring” the problem and should be taking action to save the animals.

“They were told three weeks ago and nothing has been done,” she said.

The New South Wales Department of Primary Industries is investigating the mass death.

A spokesperson said Fisheries officers had taken samples and believed extremely cold water temperatures in the lake were likely to be the cause of death.

“Officers attended Lake Conjola on Wednesday, August 6, in response to the report of dead stingrays and found 25 to 30 dead rays in the lake and up to 60 that were alive, but very cold and slow to respond,” the spokesperson said.

“Temperature samples were taken at the site, demonstrating the lake was at extremely cold levels.

“Because the area has experienced mild temperatures so far this winter, some of the stingrays were not able to survive the cold extremes.”

The spokesperson said the fish died due to the water cooling rapidly, over a short period of time and there were no visible signs of any pollutant, and no other species affected.

Resident Allan Gratzer regularly kayaks in the lake and began noticing the dead rays on the lake floor three weeks ago.

“There are more than three dozen in the entrance and more dead further up the channel,” he said.

Mrs Gratzer said a number of other lake species, such as octopus and shellfish, had decreased since the lake had closed.

“I haven’t seen an octopus for months and all the oysters are dying off,” he said.

“The lake is dying and I believe Fisheries is ignoring its responsibility.”

Shoalhaven City Councillor Patricia White said the stingray deaths were “very concerning”.

“If this was a whale washed up on the beach, we’d have people here everywhere with tractors trying to save it,” she said.

Cr White and Lakecare members claimed the rays could have escaped had the lake been open to the sea, and the tidal flow would have kept the water temperature steady.

She said council was waiting for funding and approval from the state government to dredge built up sand from the lake to create a longer-lasting opening.

Council’s Natural Resources and Floodplain Committee member Brendon Wood said, “While the death of certain marine species in an estuary may be understandably distressing to the lay person, I understand this is a normal occurrence in the dynamically changing environment”.