LONDON (AP) — London Mayor Sadiq Khan has a lot of cleaning up to do.

Khan, who made history Saturday by becoming the city’s first mayor elected to a third term, has pledged to make the River Thames swimmable.

It wasn’t a top campaign issue but it’s an audacious goal considering the waterway was declared biologically dead not long before his birth in the city in 1970 and flows as an open sewer of sorts when heavy rains overwhelm London’s ancient plumbing system.

Taming the Thames would not be Khan’s first swim upstream. His narrative is built around overcoming the odds.

As he frequently points out, he is the son of a bus driver and a seamstress from Pakistan. He grew up in a three-bedroom public housing apartment with seven siblings in South London. He attended a rough school and went on to study law. He was a human rights lawyer before he was elected to Parliament in 2005 as a member of the center-left Labour Party, representing the area where he grew up.