The Thames Tideway Tunnel is a 25 km (16 mi) combined sewer under construction running mostly under the tidal section (estuary) of the River Thames across Inner London to capture, store and convey almost all the raw sewage and rainwater that currently overflows into the estuary. These events occur when rainfall volumes exceed the capacity of Bazalgette's and other engineers' London sewerage system. The tunnelling phase of the project was completed in April 2022. Its outfall, the Lee Tunnel, runs deep under the London Borough of Newham to Beckton Sewage Treatment Works.