The  unusual occurrence was noticed several weeks ago, and the NSW Department of Primary Industries (DPI), the Environmental Protection Authority (EPA) and MidCoast Council contacted.

NSW Department of Primary Industries (NSW DPI) acting director fisheries compliance, Tony Andrews, said the large numbers of dead fish were bully mullet.

He said other species have not been impacted.

“NSW DPI is investigating the fish kill, in conjunction with the EPA and MidCoast Council,” Mr Andrews said. 

According to Mr Andrews, MidCoast Council would continue to monitor the foreshore for dead fish.

More than 500 kilograms of dead mullet have been collected by council and placed in landfill.

Waste health and regulatory services manager, John Cavanagh said council would continue to clean-up as required.

However, the number of fish found on the shore has substantially reduced over the past two days, he said.

“We understand the cause is a combination of dissolved oxygen and increased water temperatures in the area,” Mr Cavanagh said.

“With increased activity in the lake, mullet have moved to the shallows where oxygen levels are lower.

“The mullet have then become stressed and died.

“This is a natural phenomenon that occurs from time to time and we believe there is no threat to public health.”

One local resident said 10 pelicans, an osprey and possum also had been found dead on the foreshore.

He said residents and commercial fishers were very concerned about the impact the fish kill could have on both the tourism and fishing industries.

“The vast majority of commercial fishers have stopped fishing,” he said.

“People want to know what is happening to our wildlife; they want to know if the DPI will carry out a necropsy; we would like to know what the birds are dying from; we want answers.”

Mr Andrews said the fish kill was largely confined to the Symes Bay area, on the eastern end of the lake, while some dead fish have been reported as far as Brambles Reserve boat ramp.

“As a precaution, people are advised to avoid fishing in the lake, until further testing is undertaken to determine the cause and any potential risks to humans.”

Mr Andrews said there did not appear to be any obvious signs of water quality problems, however a range of tests were being undertaken to determine the cause of the fish kill.

“Samples of fish are currently undergoing testing at the Elizabeth Macarthur Agricultural Institute in Camden,” Mr Andrews said.

“Water quality samples have also been submitted for analysis.”

Both residents and visitors have posted comments on Facebook pleading with the authorities to investigate the incident thoroughly.

“Hey there, could you guys do a story on Smiths Lake and how it needs to be re-opened,” Cameron Keene posted to the Great Lakes Advocate.

“There are dead fish washing up everywhere out here because of the lack of oxygen in the water.

“The locals are fed up with the council turning a blind eye to it.”

Cindy Foley-Tennant was concerned for the health and safety of users if the dead fish and pelicans were not removed.

“As no-one seems to be caring and someone will end up getting sick because of it.”

People can report any sightings of dead fish to the NSW DPI Fishers Watch Phoneline on 1800 043 536 or can contact your local NSW DPI fisheries office if they require further information.

Over the past few weeks a number of dead mullet have been found along the northern shore of Smiths Lake.

DPI Marine Parks and EPA have been working together to identify the cause with MidCoast Council being asked to help with the clean up.