There are salmon in the Thames these days, makes a change from the era when a stomach pump was compulsory for anyone that fell in.
There used to be a couple of "beaches" beside the Thames in London, boys used to sun themselves and bathe in the waters at these places. See the Battle of Britain movie to see these boys standing knee deep in the waters and arguing over aircraft identification as dog fights and bombing took place overhead.
Just found a site about the Tower Beach which was opened in 1934:
http://www.hrp.org.uk/TowerofLondon/...cus/TowerBeach