The discovery of hundreds of dead mullet and whiting in the lake, near Cunjurong Point boat ramp, follow the lake’s closure in recent weeks. 

Residents can only speculate on what caused the mass death, but believed dredging that did not mimic the natural flow of the waterway was to blame.

However, a Department of Primary Industries spokeswoman said the fish became stranded during the receding tide. 

“The mullet have attempted to leave the lake during high tide and larger sea conditions earlier in the week. Some of the fish have become stranded in smaller backwaters during the receding tide and have died,” the spokeswoman said. 

“DPI Fisheries note that mullet undertake their annual spawning migration along the coast at this time of year.  

“The department will continue to monitor the area over the coming days.”

The DPI spokeswoman said an investigation by Fisheries and Shoalhaven City Council was underway. 

“DPI Fisheries inspected the site and observed that the main species affected is mullet, with only two individuals of two other fish species observed,” she said.

“DPI is aware of the fish kill that occurred on the South Coast at Lake Conjola entrance. The lake is currently closed to the ocean.”

The lake was dredged in early 2016, but has since closed to the ocean again. Conjola Community Association publicity officer Kristen Bird said finding the dead fish was “sad”. 

“It is another natural disaster because of the condition of the lake entrance,” she said.

“It looks a bit third world. 

“It happened last time it was closed before they dredged it with sea rays and they all died. It is affecting the fish in the lake when the lake is closed, obviously.”

Ms Bird said the natural causeway of the lake needed to be “scoured” regularly. 

“Because of various weather phenomenons, it has needed some assistance and I don’t think the assistance that has been given in recent times was correct,” she said. 

“The lake needs assistance to re-find its natural causeway, but I am not sure a one-off dredging is the answer.

“I think an ongoing scouring to help it find it’s natural causeway is the answer. 

“The most recent dredging lasted about two summers, and it did give the lake a good flushing out, but it was never going to last because they went a way the lake doesn’t naturally flow. They dredged along the northern shoreline, but the lake flows more to the southern shoreline.” 

Association vice president Dirk Trelor said dredging in 1999 lasted 13 years. 

“Dredging needs to go with the natural channel,” he said. 

“The key for the channel location is for it to be on the southern side so on the outgoing tide, it transports sand back out through the entrance.

“It is about monitoring it and doing something, rather than doing nothing. The council has to be more open to working with the natural flow of the lake.”

Data states 40,000 cubic metres of sand comes in and 30,000 cubic metres  goes out annually, leaving a surplus of 10,000 cubic metres.