The Debris Clearance Operation of the Port of London Authority removes around a thousand tonnes of litter each year from the Thames.
In the 19th century, sewage in the Thames was so bad that 1858 was known as the year of the Great Stink.
Since recent cleaning of the river, 119 species of fish have been found in the Thames.
There are 396 sewage works along the Thames, cleaning the sewage and returning the water to the river. This is necessary because a drop of rain falling into the Thames at its source may have been drunk by as many as eight people before it reaches the sea.