The Thames Tideway Tunnel is a deep-level sewer along the tidal section of the River Thames in London, running 25 kilometres from Acton in the west to Abbey Mills in the east, where it joins the Lee Tunnel which connects to Beckton Sewage Treatment Works. The tunnel is designed to capture almost all the raw sewage and rainwater from combined sewers which would otherwise overflow into the river during heavy rain. The sewage can be stored in the tunnel until it can be treated at Beckton.