This is why the River Thames is so brown in London

... The River Thames - the huge stretch of water that runs through our capital. ...
... According to Visit Thames, the River Thames may take its name from the Sanskrit Tamas, meaning 'dark' as its waters are often cloudy and dark. ...
... The tunnel will be 25km long when completed and prevent the tens of millions of tonnes of pollution that currently pollute the River Thames every year. ...
... So, it seems unlikely that we will ever have a crystal clear River Thames. ...