A species of fish is returning to the Lower Lakes and Coorong.

The Department for Environment and Water's Adrienne Rumbelow said the number of black bream in the area had been in severe decline since the late 1980s

"The commercial fishery catch of black bream in the Coorong over the last nine years has been only 5 per cent of what it was in the mid 1980s," Ms Rumbelow said.

"The ecosystem of the Coorong is still recovering post-drought, and this includes populations of long-lived fish like black bream."

Ms Rumbelow said late last year commercial fishers told the Department they had spotted adult female black bream below the barrages.

"The tip prompted us to work with local scientists and the community to manage environmental water during spring and summer to maintain barrage releases and improve water quality in the Coorong," she said.

Water releases helping fish

About 500 gigalitres of environmental water has been released into the Coorong in recent months.

"The environmental water to the Coorong was critical in creating a salt wedge, which is an area where freshwater sits above saltwater," Ms Rumbelow said.

"Salt wedges are needed to keep black bream eggs and larvae buoyant and they also provide food for larval fish to develop and grow."

That tactic appears to have been successful.

More than 100 black bream fingerlings were recorded at sites throughout the area in March and April.

Baby black bream from the Coorong. ( Supplied: SA Environment and Water Department )

Associate Professor Qifeng Ye from the South Australian Research and Development Institute (SARDI) said it was a fantastic result.

"These fish were most likely spawned during late spring and summer, and the environmental water released through the barrages helped create suitable nursery conditions for this species," Associate Professor Ye said.

She said it was a good sign towards the recovery of an iconic fish species.

"However, we still have a long way to go before these baby black bream are mature and can help rebuild the population in the Coorong.