or Old Father Thames. The Thames, so far as it belongs to London.
Say, Father Thames, for thou hast seen Full many a sprightly race Disporting on thy margent green, The paths of pleasure trace.
The epithet is not uncommonly applied to other great rivers, especially those on which cities are built. The river is the father of the city, or the reason why the site was selected by the first settlers there.
O Tiber, Father Tiber, To whom the Romans pray.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894