New River (abandoned)

Quote "The New River has an unhelpful name, being neither new nor a river! It is a water supply aqueduct, completed in 1613, to bring drinking water from Hertfordshire to North London. Before this time, London’s water supply was limited to the Thames, local streams and wells which were often contaminated. Thames Water has worked with partners to create a 28 mile long-distance path that follows the river’s course."
This picture is of a section abandoned in the mid-1800s when the course was shortened, leaving this spur running through Whitewebbs Park. The bed is still carrying some watergrasses after many years of no water.

More enlightening information to be found here