Resident of the area for 30 years Neil Fisher noticed a large number of dead bream on Tuesday morning while walking his dog along the foreshore.

“I saw three sea eagles down getting a feast on some decent sized bream,” the 67-year-old said.

“On Saturday we noticed leatherjackets coming up to the surface for air, and this morning I counted 50 dead bream in just 50 metres.

“If you counted them there could be thousands, and I didn’t even know there was this sized bream even in here.”

The NSW Department of Primary Industries said fisheries received reports of the large fish kill, with investigations on Monday confirming hundreds of dead snapper and six spined leatherjackets washed up along the lake’s edge.

“On-going investigations by DPI Fisheries and Bega Valley Shire Council have confirmed poor water quality as the suspected cause,” a DPI spokesperson said. 

“Results received today from comprehensive testing by council has indicated dissolved oxygen levels are poor throughout the lake and in some locations below levels able to support aquatic life.

“This poor water quality is suspected to be the result of run-off from recent heavy rain in the catchment of Wallagoot Lake.”

Fisheries said it is continuing to work alongside council on assessing the fish kill, and is predicting further deaths to occur unless the water quality improves. 

Mr Fisher said locals noticed an unusual smell coming from the lake a week ago.

“We knew something was going on in the lake because recently it had gone from a rusty red algae colour to a khaki green,” he said.

“It was starting to smell, which was unusual. It smells like rotting seaweed.

“The lake is usually cleaner than it is at the moment.”

Since he moved to the lake in 1989, he says only a number of dead pufferfish on the foreshore 15 years ago compares to what he has witnessed this week.

“We thought there must be a lack of oxygen caused by something,” Mr Fisher said.

“The water had been really warm and something’s made the algae take off.

“The mouth of the lake has been closed for about a year and a half now and it’s significantly lower than it usually is from basically a lack of rain.”

Bournda Environmental Education Centre principal Doug Reckord said water in the lake is at low level despite recent rain.

“It’s not a nice sight, and I felt for the locals out west who have millions of dead fish on their hands including massive cod,” he said.

“Wallagoot Lake is classified as a mature ‘wave dominated estuary’, which means that with a very small catchment feeding the lake, the lake tends to stay closed for long periods of time.

“This is reflected in data which shows it stays closed for longer than any other estuary on the south coast and when it opens, naturally or artificially, it is rapidly closed by wave action.

“The central basin of the estuary is an efficient trap for sediment and pollutants, which is a constraint on development activity in the catchment.”