What are the main rivers in the United Kingdom?

As an American, the Thames of London and the Mersey of Liverpool are the only ones that I am aware of. An English contributor will have to tell you of any others.

Tweed, Tay, Forth, Clyde, Spey, Moray, Avon, Ouse, Severn, Humber, Trent, Tees, Tyne...

The rivers mentioned by other contributor above, plus:

Eden, Ure, Lune, Wharfe, Derwent, Dee, Aire, Wye, Great Ouse, Stour, Medway, Clwyd, Conwy, Erne, Blackwater.