Boondelbah Island, also known as the Boondelbah Nature Reserve, is a protected nature reserve and uninhabited island lying 2 kilometres (1.2 mi) off the mouth of Port Stephens on the coast of New South Wales, Australia. The 14-hectare (35-acre) reserve and island is one of two breeding sites of the nominate subspecies of the threatened Gould's petrel and, with the nearby Cabbage Tree Island which hosts the principal colony, has been classified by BirdLife International as an Important Bird Area. Both Boondelbah and Cabbage Tree Islands are gazetted nature reserves under the National Parks and Wildlife Act, 1974 (NSW), so protecting the islands' habitat from land uses incompatible with nature conservation. Access is only permitted for scientific and conservation purposes.