The Fleet was once called the River of Wells because there were so many wells along its course, some of them holy. It was also surrounded by various religious foundations, monasteries, convents, and friaries. Henry VIII erected Bridewell Palace along its banks, but his son Edward VI gave it to the City of London to serve as a school for boys and a house of correction for women of ill repute. An interesting juxtaposition of functions. "Bridewell" later became a general house of correction for many types of offenders, and the term became generic for such institutions.
One reason the royals gave up Bridewell was probably the fact that the river had become an open sewer, clogged with animal carcasses from nearby Smithfield Market, refuse from tanneries, and the wastes and castoffs of untold numbers of Londoners.
The noxious miasmas that Fleet Ditch -- as it was renamed -- exhaled may be the reason why it was surrounded by hospitals, prisons, workhouses, and cheap housing. It was a good place for thinning out the poor and undesirable. Many criminals had their haunts along or near its banks.Dickens placed Fagin's den in nearby Field Lane on Saffron Hill.
The Fleet river/ditch/sewer was gradually covered in the eighteenth and nineteenth centuries. Water still flows there underground, and it empties into the Thames under Blackfriars Bridge.