[T]he waters of the Fleet were renowned for being clear and sparkling. As the medieval city began to grow, mills, tanneries and meat markets sprang up along its banks. Water was vital to keep these industries functioning and growing and gradually the river was polluted with blood, sewage and other waste â€“ it effectively became a waste tip, a handy repository to discard anything unwanted including the carcasses of dead livestock.
As a result, over the years the river became shallower and the water much slower than in previous generations, only exacerbating the burgeoning problem of the health hazard it now presented. It would silt up in the summer and although the spas and wells upstream remained open and functioning the Fleet in the city of London became an open sewer with a mix of slums and prisons on its banks. Something had to be done.
The Great Fire of London in 1666 provided that opportunity. The architect Sir Christopher Wren was afforded the chance of transforming the lower Fleet.
By 1680 this part of the river had been turned in to the New Canal. It was hailed as the Venice of England but its days were numbered from the very beginning.
It was poorly used as a canal and, despite its new clothes, it still stank to high heaven. … Within a generation it was no longer fit for purpose as a canal.
The river was channelled underground in the 1730s from Holborn to Fleet Street, which still bears its name. Decades later it was filled in and arched over from Fleet Street down to the river Thames and is covered by what is now New Bridge Street. …
[T]he final blow was to come in the 1860s. It was at this point that the sunken river was incorporated in to the new network of sewers â€“ an astonishing piece of industrial scale engineering designed by the visionary civil engineer Joseph Bazalgette. A little later its upper reaches in Hamstead and Kentish Town disappeared forever as well.
Via Fred Lapides.