Andrew Mitchell, CEO of Tideway, said even once the sewer is completed, the Thames will still look brown. He said it is because it is a muddy river, owing to the silt on the riverbed. But he added new water that enters the system will be clean "almost overnight".

Is there poop in the River Thames?

Around 39 million tonnes of sewage flow into the Thames every year. A massive, new sewer is being built to fix that – but is it enough? There's a lot of poop in London and not enough places to put it. ... Around 39 million tonnes of sewage flows into the River Thames each year.

How clean is the Thames in London?

The Thames is considered to be the cleanest river in the world that flows through a major city. The Thames is home to 125 species of fish and more than 400 invertebrates. This is in spite of the fact that raw sewage is routinely pumped into the river during heavy rains.