Cockatoo Island is the largest island in Sydney Harbour in Sydney, New South Wales, Australia. It is at the junction of the Parramatta and Lane Cove rivers. Cockatoo Island has been a prison, industrial school, and reformatory (a prison for boys). It was also the site of one of Australia's biggest shipyards during the 20th century. The first of its two dry docks was built by convicts in 1857. The dockyards closed in 1992.