Although it may be hard to spot through the thick silt, mud and sand, the River Thames is home to some 125 different species of fish. Stretching from Teddington Lock in the west out to the Thames Estuary, some of the more well-known varieties include seabass, sole and even trout.

The river is also home to some more obscure fish, such as the zander or the cucumber-smelling smelt. Many of the fish that live in the Thames are migratory, making their way up to London from as far afield as Siberia.

_{Image: The smelt © Wikimedia Commons}

Famously, on 19 January 2006, a northern bottlenose whale swam up the river to Battersea, after losing its way in the North Sea. The six-metre-long female whale can now be seen in the Natural History Museum.  

The Thames is also home to a vast array of other mammals. Seals make up a huge part of the ecology, numbering close to 4000 across the two species of harbour and grey seals. Even though most of these seals live on sandbanks and coastal creeks, some have been sighted following fish as far west as Richmond. 

_{Image: A grey seal pup © Alastair Rae/Wikimedia Commons}