The
River Lea (or
Lee) in
England originates in Marsh Farm,
Leagrave,
Luton in the
Chiltern Hills and flows generally southeast, east, and then south through east
London where it meets the
River Thames, the last section being known as
Bow Creek. It is one of the largest rivers in London and the easternmost major tributary of the Thames. Its
valley creates a long chain of marshy ground along its lower length, much of which has been used for gravel and mineral extraction, reservoirs and industry. The river has been canalised to provide a navigable route for boats into eastern Hertfordshire, known as the
Lee Navigation. While the lower Lea remains somewhat polluted, its upper stretch and tributaries, classified as
chalk streams, are a major source of drinking water for London. A diversion known as the
New River, opened in 1613, abstracts clean water away from the lower stretch of the river for drinking. Its origins in the Chilterns contribute to the extreme
hardness (high mineral content) of London tap water.