Clark Island is a small island in Sydney Harbour, lying on the coast of New South Wales, Australia. Forming part of the Sydney Harbour National Park, the island lies offshore of the Sydney suburb of Darling Point, in the eastern section of the harbour between the Harbour Bridge and the harbour entrance. It is 0.9 hectares in area. Although the island is uninhabited, facilities include picnic tables, toilets, and drinking water. No ferry services operate to the island.
The island derives its name from Lieutenant Ralph Clark, an officer of the First Fleet. In the early days of New South Wales, naval officers were allowed to keep their own vegetable gardens, which were tended by convicts. Clark established one such garden on the island, which was unsuccessful as any produce was soon stolen as a result of the limited rations available at the time. In February 1790, Clark noted that "some Boat had landed since I had been there last and taken away the greatest part … it is impossible for any body to attempt to raise any Garden stuff here, before it comes to perfection they will steal it.