 Further downstream, the channel merges with the River Lea to become the man-made, concrete-banked River Lee Diversion as it skirts the eastern perimeter of the King George V Reservoir, the first of the Lee Valley Reservoir Chain, and then the William Girling Reservoir.The river forms the boundary of the London Borough of Enfield and Waltham Forest and the historical boundary between Middlesex and Essex.Flowing under the North Circular Road and close to Banbury Reservoir, it splits from the River Lee Diversion to cross Tottenham Marshes, and passes close to the Lockwood Reservoir, High Maynard Reservoir and Low Maynard Reservoir.