The Fleet River is a small river in central London, England. It flows for about 7 miles, starting from Fleet Street and eventually joining the River Thames. Historically, it was an important waterway for trade and transportation, but much of it has been covered over and is now underground. The river's name is derived from the Old English word "flet," meaning "stream" or "river." Today, the Fleet River is mostly hidden, with only a few visible sections, such as Clerkenwell Green. It serves as a reminder of London's natural waterways and their historical significance.