It originates in Bedfordshire, in the Chiltern Hills, and flows southeast through Hertfordshire, along the Essex border and into Greater London, to meet the River Thames at Bow Creek.

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.

The Lea's origin in the Chilterns contributes to the extreme hardness (high mineral content) of London tap water.

[3][4] A simpler derivation may well be the Brythonic word cognate with the modern Welsh "Li" pronounced "Lea" which means a flow or a current.

In the Iron Age the Lea and Stort valleys formed a hotly contested frontier zone between the Catuvellauni to the west and the eastern Trinovantes.

From around the ninth or tenth century, and the establishment of counties in this part of England, the Lea-Stort line has formed the historic boundary between Essex to the east and Hertfordshire and Middlesex to the west.

They have compromised on this further south, on the lower Lea, where the quality and quantity of cross-river links is much greater, and the communities on either side better integrated as a result.

The Stort, the most important tributary of the Lea, joins a short distance from Hertford at Feildes Weir, and is itself navigable as far upstream as Bishops Stortford.

On the eastern side the river passes Waltham Abbey on the largely rural Essex bank, and then Chingford and Walthamstow in east London.

Around Bow Creek, major industry prevailed, including the Thames Ironworks, Bromley-by-Bow Gasworks and West Ham Power Station.

The river was historically tidal as far north as Hackney Wick, but now the tide is held back by the Bow Locks between Bromley-by-Bow and West Ham.

The lower Lea was at that time a wide, tidal and unchannelled river, so the construction of the bridge allowed a far greater degree of social and economic integration between Essex on one side and Middlesex (including the City of London) on the other than had been possible before.

It was the channels created for these mills that caused the Bow Back Rivers to be cut through the former Roman stone causeway at Stratford (from which the name is derived).

The River Lea flows through the old brewing and malting centre of Ware, and consequently transport by water was for many years a significant industry based there.

Bargemen born in Ware were given the "freedom of the River Thames" — avoiding the requirement of paying lock dues — as a result of their transport of fresh water and food to London during The Great Plague of 1665–66.

[16] The extensive level of waterborne trade led the historian John Stow, writing in 1603, to describe the Lea as “this pleasant and useful river”.

[17] The riverside has hosted a number of major armaments manufacturers, such as the Waltham Abbey Royal Gunpowder Mills, the Royal Small Arms Factory at Enfield Lock (which is now a housing development known as Enfield Island Village) and the Congreve Rocket Factory on the site of Stratford Langthorne Abbey.

In 2009, Three Mills Lock was installed on the Prescott Channel to maintain water levels on the Lea, within the park at a depth of 2 metres (7 ft).

In 894, a force of Danes sailed up the river to Hertford,[23] and in about 895 they built a fortified camp, in the higher reaches of the Lea, about 20 miles (32.2 km) north of London.

After inconclusive clashes with the Tower Hamlets Militia and other Parliamentarian forces, an engagement known as the Battle of Bow Bridge, the Royalists headed for Colchester and were besieged there.

[27] The ecological, landscape and recreational importance of the river and its surrounding land has been recognised through inclusion in a number of parks and by several planning policy designations.

[30] Vice Magazine suggested that Wells' story may have been invented to publicise authorities' attempts to evict houseboats from the area that year, ahead of the 2012 Olympic Games.

[33] The sewage pollution, as well as that of fertiliser washed in from agricultural fields causes eutrophication, an excess of nutrients, which not only unbalances the ecosystem, but also leads to de-oxygenation of the water.

[34] In April 2021, Hackney Council wrote to the Environment Agency calling for action to address sewage discharge and pollution in the river.

There are a number of theories about the identity of the Fair Lady, including the idea that it may refer to Matilda,[38] the builder of Bow Bridge and its neighbours, or that it may apply to the River Lea itself.

[42] In 2014, German writer Esther Kinsky published a novel, Am Fluß, now available in English as River, translated by Iain Galbraith,[43] based around her walks along the lower Lea from the marina at Horseshoe Point to its confluence with the Thames.