In Pictures: London's new 'super sewer' to end Thames pollution blight

London's existing sewerage network dates back to the second half of the 1800s. With the size of the population set to continue to swell, the need for the £4.3-billion ($5.6-billion) upgrade has become critical.

Thousands of engineers and construction staff have spent the past seven years creating the biggest-ever upgrade to the city's 19th-century sewers.

A statue of Saint Barbara, patron of tunnelling, inside a shrine on the Thames Tideway tunnel building site, in west London.

A large concrete shaft, part of the Thames Tideway tunnel in west London.

The new 25-kilometre (15-mile) "super sewer" is 7.2 metres in diameter and snakes from west to east following the curves of the river.

A civil engineer walks inside a 7 metre concrete tunnel at the Thames Tideway building site, in west London.

Builders work at the Thames Tideway tunnel building site, in west London.

When operational, it will carry sewage only when rain means the existing sewers are full to overflowing.

Civil engineers work next to a 7 metre wide concrete tunnel at the Thames Tideway building site, in west London.

At its height, 10,000 people were working on the project, which has seen six tunnel-boring machines forge through three distinct geologies - clay in the west of the city, sand and gravel in the centre and chalk in the east.