River Fleet

The River Fleet was a largely underground river that emptied into the River Thames at Blackfriars Bridge in London. The Fourth Doctor knew its exact course, as he had once caught a salmon there with the Venerable Bede. (TV: The Talons of Weng-Chiang)

The Eighth Doctor later commented that, of all London's subterranean rivers, the Fleet was the one most associated with evil. (AUDIO: Dead London)