The eastern freshwater cod has been described as "just as important as a crocodile or white shark". Now, experts have designed a nesting box that has delivered promising results.

The discovery of thousands of eastern freshwater cod spawn inside a specially designed nesting box was the culmination of years of work by NSW Local Land Services and the Department of Primary Industries.

While evidence of cod breeding was found in only one box, Mr Morris said that one success will make a significant difference to the wild population of which there is thought to be less than 250 adult cod.

The eastern freshwater cod is one of four freshwater cod species in Australia listed as either vulnerable or endangered by the federal government.

Mr Morris is confident the recent success in breeding wild eastern freshwater cod could help efforts to save the other species.

"Any benefit that we get to the breeding outcomes of eastern freshwater cod will extend to Murray cod, trout cod, and hopefully Mary River cod as well," Mr Morris said.