River users are being urged to fish the Swan and Canning rivers for prawns and then document their catch as scientists battle to reinstate a once-popular Perth pastime.

In a world-first, researchers have artificially bred western school prawns in the laboratory and then released more than 300,000 of them into the wild.

Prawning on the Swan River was once a popular river activity but over-fishing and pollution pushed the species to the brink of collapse.