The Lea Valley, the valley of the River Lea, has been used as a transport corridor, a source of sand and gravel, an industrial area, a water supply for London, and a recreational area. The London 2012 Summer Olympics were based in Stratford, in the Lower Lea Valley.
The northern section of the valley, although including several towns (Luton, Harpenden, Hertford and Ware), is mainly rural. Below Hertford the Lea flows on a wide floodplain, which becomes an increasingly urban transport corridor as it enters London. Many of the upper sections have been exploited for sand, gravel or brickearth, and are now part of the Lee Valley Park.
From Hoddesdon a more or less continuous ribbon development runs south to the west of the river, running through Wormley, Broxbourne, Cheshunt and Waltham Cross to Freezy Water. To the south the wider expanse of London includes the floodplain settlements of Enfield Lock, Enfield Highway, Brimsdown, Ponders End, Edmonton, Tottenham, Tottenham Hale, Clapton, Lea Bridge, Leyton, Hackney Wick, Old Ford, Bow, Stratford, West Ham, Bromley, Canning Town and Leamouth.
A combination of factors led to the development of the valley as an important industrial area. These included, in the early days, distance from London for noxious industries and the availability of water power. Later factors included cheap electrical power from Brimsdown and large expanses of flat land.
The valley as a boundary
In earlier centuries the river Lea and its marshland formed a natural boundary between the historic areas of Middlesex and Essex, some 2 km wide and 20 km long. The river was crossed at several points by fords or ferries, which were eventually replaced by bridges. At Stratford a stone causeway on the Roman road to Colchester was supplemented by bridge in 1100. In 1745 the valley was crossed at Clapton by Lea Bridge. In 1810 an iron bridge was built linking East India Dock Road. In the late 1920s the Lea Valley Viaduct, carrying the North Circular Road, was built to a design by Owen Williams. This was replaced in the 1980s.
The valley as a route
The valley of the Lea formed a route followed by the New River and Lee Navigation, and roads including the Roman Ermine Street, the Hertford Road (A1010) and the later Great Cambridge Road (A10) and A1055. The valley is also followed by two routes of what became the Great Eastern Railway and had important marshalling yards and locomotive works at Temple Mills.
Much early industrialisation was a result of the availability of water power for numerous mills. These include the Waltham Abbey Royal Gunpowder Mills (originally a fulling mill but already producing gunpowder by 1665), the 19th century Royal Small Arms Factory at Enfield and Wright's Flour Mill (London's last surviving working mill) at Ponders End. Further south at Bow is the Three Mills tidal complex.
In the 18th century Bow porcelain factory flourished. In the 19th century the lower Lea became an important area for the manufacture of chemicals, in part based on the supply of by-products such as sulphur and ammonia from the Gas Light and Coke Company's works at Bow Common. Other industries included Bryant and May, Berger Paints, Stratford Railway Works and confectionery manufacturer Clarnico (later Trebor). Where the river meets the Thames were the Orchard House Yard and Thames Ironworks shipyards.
In the 20th century the combination of transport, wide expanses of flat land and electricity from riverside and canal-side plants such as Brimsdown, Hackney, Bow and West Ham led to expansion of industries including for example Enfield Rolling Mills and Enfield Cables, Thorn Electrical Industries, Belling, Glover and Main, MK Electric, Gestetner, JAP Industries, Ferguson Electronics, Hotpoint, Lesney (original makers of Matchbox toys), a Ford components (later Visteon) plant and Johnson Matthey. Much industry has now gone, replaced by warehousing and retail parks.
Market gardening and nurseries
North of Cheshunt the Lea Valley, particularly around Nazeing, is associated with market gardening, nurseries and garden centres. The industry once dominated the area from Ponders End, north through Enfield Lock, Waltham Cross and Cheshunt, to Wormley, Turnford and Nazeing, and spawned industries such as Pan Britannica Industries. In the 1930s the valley contained the largest concentration of greenhouses in the world.  Stamp writing in 1948 described how glasshouses, originally established on the 'warm brickearth soils' of Tottenham and Edmonton in the 1880s, had been progressively driven north into the often poorer soils further north by the growth of London. At the same time the growth of industry had intensified the lack of winter sunshine. Today, in most parts south of Cheshunt greenhouses have been replaced by residential areas.
The Lee Valley Park occupies large areas of the valley. An extensive area of open land, built up using rubble from the Blitz, is Hackney Marshes. By contrast, Walthamstow Marshes is retained as a Site of Special Scientific Interest (SSSI).
The valley became very important for London's water supply, as the source of the water transported by the New River aqueduct, but also as the location for the Lee Valley Reservoir Chain, stretching from Enfield through Tottenham and Walthamstow.
- 'Hackney: Communications', A History of the County of Middlesex: Volume 10: Hackney (1995), p. 4-10, retrieved 14 February 2011 Text "web" ignored (help)
- "The Iron Bridge Over The River Lea, 1810 (p. 126)", Survey of London vol=43 and 44: Poplar, Blackwall and Isle of Dogs (1994): XI–XX, retrieved 14 February 2011 Text "ref" ignored (help)
- Lea Valley Viaduct, site of, retrieved 2011-02-14 Text "web " ignored (help)
- Jim Lewis 1999, London's Lea Valley, Phillimore, ISBN 1-86077-100-9
- History of the Lea Valley greenhouse industry Retrieved 23 November 2012
- Stamp, Laurence Dudley (1948). The Land of Britain - Its Use and Misuse (1 ed.). London: Longmans, Green & C Ltd. p. 142.