In the early 19th century the River Thames was practically an open sewer, with disastrous consequences for public health in London, including numerous cholera epidemics. Proposals to modernise the sewerage system had been put forward in 1856, but were shelved due to lack of funds. However, after The Great Stink of 1858, Parliament realised the urgency of the problem and resolved to create a modern sewerage system.
Joseph Bazalgette, a civil engineer and Chief Engineer of the Metropolitan Board of Works, was given responsibility for the work. He designed an extensive underground sewerage system that diverted waste to the Thames Estuary, downstream of the main centre of population. Six main interceptory sewers, totalling almost 100 miles (160 km) in length, were constructed, some incorporating stretches of London's 'lost' rivers. Three of these sewers were north of the river, the southernmost, low-level one being incorporated in the Thames Embankment. The Embankment also allowed new roads to reduce traffic congestion, new public gardens, and the Circle Line of the London Underground.
The intercepting sewers, constructed between 1859 and 1865, were fed by 450 miles (720 km) of main sewers that, in turn, conveyed the contents of some 13,000 miles (21,000 km) of smaller local sewers. Construction of the interceptor system required 318 million bricks, 880,000 cubic yards (670,000 m³) of concrete and mortar, and excavation of over 3.5 million tonnes of earth.
Gravity allows the sewage to flow eastwards, but in places such as Chelsea, Deptford and Abbey Mills, pumping stations were built to raise the water and provide sufficient flow. Sewers north of the Thames feed into the Northern Outfall Sewer, which feeds into a major treatment works at Beckton. South of the river, the Southern Outfall Sewer extends to a similar facility at Crossness.
In the 20th century, major improvements were made to the sewerage system to reduce pollution of the Thames Estuary and the North Sea.