Garden Island is a slender island about 10 kilometres (6 mi) long and 1.5 kilometres (0.9 mi) wide, lying about 5 kilometres (3 mi) off the Western Australian coast, to which it is now linked by a man-made causeway. Like Rottnest Island and Carnac Island, it is a limestone outcrop covered by a thin layer of sand accumulated during an era of lowered sea levels. The Noongar Indigenous Australians tell of walking to these islands in their Dreamtime. Garden Island is home to a tammar wallaby population.