Whish!

The Thames, until the 19th Century, an open sewer which led to cholera : water in, water out.  By the 1850s London's population surpassed two million , all using the river for, which had become so God awful that the smell alone closed government  - rugs hung from Parliament windows to block the foul elements.  

Enter Joseph Bazalgette, a civil engineer and Chief Engineer of the Metropolitan Board of Works, who was tasked with moving a lot of shit.  Without him, London could not have remained the world's most populated city until '52 when Tokyo became bigger (London peaked BTW at 8.6 million in 1939 ; today the city holds around 7.8 million, 24th in the world, according to the UN).

Balagette's sewage network, in operation today my goodness, moves waste along the Thames Valley corridor to the Thames Estuary via six main interceptor channels totalling 100 miles and constructed from 1859 and 1865; They, in turn, fed by 450 miles of main sewers that shift contents from 13,000 miles of local pipes. Construction of the interceptors required 318 million bricks, 2.7 million cubic metres of excavated earth and 670,000 cubic metres of concrete.  Gravity allows the sewage to flow eastwards along the Thames Corridor.

During the 20th century, modernisation reduced pollution of the Thames Estuary and North Sea.  Otherwise not much has changed, pictured excluded.