The Toronto Islands were not always islands but actually a series of continuously moving sand-bars, or littoral drift deposits, originating from the Scarborough Bluffs and carried westward by Lake Ontario currents. By the early 1800s, the longest of these bars extended nearly 9 kilometres south-west from Woodbine Avenue, through Ashbridge's Bay and the marshes of the lower Don River, forming a natural harbour between the lake and the mainland.