Hackney Marshes is an area of grassland on the western bank of the River Lea in the London Borough of Hackney. It was incorporated into the Lee Valley Park in 1967. It was originally a true marsh, but was extensively drained from Medieval times, and rubble was dumped here from buildings damaged by air raids during World War II.The principal area of the marsh lies below Lea Bridge Road between the Old River Lea, and the Hackney Cut - an artificial channel of the Lee Navigation, dug about 1770, to avoid a loop in the natural watercourse. The southern extent is marked by the A12; although the industrial land around Hackney Wick Stadium was originally an extension of the marsh, it now forms a part of the Olympic Park for the 2012 Summer Olympics.Hackney Marsh is one of the largest areas of common land in Greater London, with 136.01ha of protected commons.