In the poem 'Composed Upon Westminster Bridge' William Wordsworth uses personification to depict the city, the river and the business heart of the city.
The line 'the river glideth at his own sweet will' refers to the autonomy that Nature has - always used by, but still more powerful than, man. Yes London is big, powerful and man-made but it can only use the river, not control it nor divert it, nor make it flow faster or slower. He may have been comparing, thinking back and reminiscing about his own Lakeland mountainous river 'The Derwent' which hurried and babbled its way past his childhood home. This river could be a life-threatening dangerous torrent (as has been the case this mionth in th UK where it has taken lives, including that of a police officer in the floods.)
The River Thames glides by because it chooses to, not because it is under London's control. Yes, we have the multi-million pound Thames Barrier in case of flooding nowadays, but the jury is out on whether that will be any match for a global warming tsunami coming up the Thames estuary or the Thames in a climate change spate. Wordsworth was always aware of the terrible force of danger that lay behind the beauty of Nature - how right he was.