The turtle you found in your backyard in western Sydney is likely one of several species native to Australia. If it is a small freshwater turtle, it may be a Sydney Swamp Turtle (Myuchelys georgesi), which is commonly found in eastern Australia, or it could be an Eastern Long-necked Turtle (Chelodina longicollis). Both species are often spotted in suburban areas, especially around ponds, rivers, and wetlands.
To accurately identify the species, consider its size, shell shape, coloration, and habitat. If possible, you could take a picture and compare it to online resources or consult a local wildlife expert or reptile enthusiast. It’s also important to handle wildlife with care and ensure that the turtle is safely returned to its natural habitat if it’s not a domestic pet.
