The 16-mile tunnel across central London will capture raw sewage that would have spilled into the...
Major construction work on London's £5bn super sewer is about to be completed.
Known officially as the Thames Tideway Tunnel, it has been designed to reduce the amount of raw sewage that flows into the river.
"This is the moment we've all been waiting for," Andy Mitchell the CEO of Times Tideway told BBC News from a boat above the tunnel on the Thames.
Raw sewage under normal conditions goes to wastewater treatment plants but currently, even a small amount of drizzle in London can overwhelm the network, triggering overflows into the Thames.
The new super sewer will mean that instead of flowing into the river, almost all sewage overflows in the centre of London will be stored in the tunnel until it can be processed.
The 7.2m wide tunnel flows steadily downhill from Acton in west London to Abbey Mills in the east and during periods of sustained rainfall it will fill up with a mix of raw sewage and storm water.
After testing over the summer the super sewer will be handed over to Thames Water, a water company about £15bn in debt and dogged by constant rumours of financial problems.
"We have had our challenges. It's absolutely fair to say that." Tessa Fayers, Thames Water's operations director for Thames Valley and Home Counties, told BBC News."But I think one of the things if you go back in our heritage back to the 1800s Thames Water is phenomenal at delivering infrastructure solutions that provide fantastic sanitation services to the city of London."
Though the super sewer is one of the biggest upgrades to London's sewage network since it was built by Joseph Bazalgette in the 1860s, it is unlikely to be a permanent solution.
"The super sewer is a massive, expensive pipe and I think the Victorians would be a bit embarrassed that we haven't come up with a more modern solution than that," says Theo Thomas from campaign group London Waterkeeper.