Cockburn Sound (Nyungar: Derbal Nara)[1] is an inlet of the Indian Ocean on the coast of Western Australia.

It extends from the south of the mouth of the Swan River at Fremantle for about 25 kilometres (16 mi) to Point Peron near Rockingham.

The sound was named in 1827 by Captain James Stirling, probably after Admiral Sir George Cockburn.

Reports from 2010 suggest the monitoring of pollutants was not adequate, using degradation of sea-grass since 2005 as a key indicator.

[4] Media coverage in December 2016 indicates the leaking of firefighting chemicals from the local defence base at Garden Island could be a factor,[5] however the report was only made available in September 2016.