How the Thames made an extraordinary recovery over 60 years.

It might surprise you to know that the River Thames is considered one of the world’s cleanest rivers running through a city. What’s even more surprising is that it reached that status just 60 years after being declared “biologically dead” by scientists at London’s Natural History Museum. Yet despite this remarkable recovery, there’s no room for complacency – the Thames still faces new and increasing threats from pollution, plastic and a rising population.

The Thames runs 229 miles from Kemble in Gloucestershire to Southend-on-Sea in Essex, where it flows into the North Sea. Where it bisects London, it has experienced pressures from expanding numbers of citydwellers since medieval times.

The river became a repository for waste, with leaking cesspits and dumped rubbish reducing many of its tributaries to running sewers. Many of these small rivers now lie underneath the streets of London, long covered up to hide their foul smells: the Fleet, which runs from Hampstead and enters the Thames at Blackfriars, is probably the best known.

The final straw was the hot summer of 1858 – referred to as the Great Stink – when the high levels of human and industrial waste in the river actually drove people out of London. The civil engineer Sir Joseph Bazelgette was commissioned to build a sewage network to alleviate the problem, which is still in use today. What followed was over a century of improvements to the network, including upgrading sewage treatment works and installing household toilets linked to the system.