The Stain Hill Reservoirs lie to the north of the River Thames

River Thames

The River Thames flows through southern England. It is the longest river entirely in England and the second longest in the United Kingdom. While it is best known because its lower reaches flow through central London, the river flows alongside several other towns and cities, including Oxford,...

 near Kempton Park Racecourse

Kempton Park Racecourse

Kempton Park Racecourse is a horse racing track in Sunbury-on-Thames, Surrey, England, which is a western suburb of London 16 miles from the city centre. The site is set in of land....

 between Kempton Park

Kempton Park, Surrey

Kempton Park is a locality in the Spelthorne district of Surrey, which is the location of Kempton Park Racecourse.Kempton Park appears on the Middlesex Domesday Map as Chenetone. It was held by Robert, Count of Mortain...

 and Hampton

Hampton, London

Hampton is a suburban area, centred on an old village on the north bank of the River Thames, in the London Borough of Richmond upon Thames in England. Formerly it was in the county of Middlesex, which was formerly also its postal county. The population is about 9,500...

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The reservoirs were built by the Southwark and Vauxhall Waterworks Company

Southwark and Vauxhall Waterworks Company

The Southwark and Vauxhall Waterworks Company was a utility company supplying water to parts of south London in England. The company was formed by the merger of the Southwark and Vauxhall Water Companies in 1845 and became part of the publicly-owned Metropolitan Water Board in 1903.-Southwark Water...

 and are now managed by Thames Water

Thames Water

Thames Water Utilities Ltd, known as Thames Water, is the private utility company responsible for the public water supply and waste water treatment in large parts of Greater London, the Thames Valley, Surrey, Gloucestershire, Wiltshire, Kent, and some other areas of in the United Kingdom...

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The reservoirs are no longer used for pre-treatment water storage, but are now used for the storage of wash water from the adjacent treatment works to allow the settlement of solids out of suspension. The water is then discharged to Sunnyside reservoir for further settlement before being discharged back to the river Thames.

Stain Hill has significant populations of moulting and wintering waterfowl

Waterfowl

Waterfowl are certain wildfowl of the order Anseriformes, especially members of the family Anatidae, which includes ducks, geese, and swans....

, particularly where the water is shallow and marginal vegetation has developed. There are nationally significant numbers of shoveler

Shoveler

The shovelers, formerly known as shovellers, are four species of dabbling ducks with long, broad spatula-shaped beaks:* Red Shoveler, Anas platalea* Cape Shoveler, Anas smithii* Australasian Shoveler, Anas rhynchotis...

 and gadwall

Gadwall

The Gadwall is a common and widespread duck of the family Anatidae.- Description :The Gadwall is 46–56 cm long with a 78–90 cm wingspan. The male is slightly larger than the female, weighing on average 990 g against her 850 g...

in late winter. The dry concrete banks support one of the UK's largest populations of the nationally scarce plant tower mustard (arabis glabra), a UK Biodiversity Action Plan Priority species. Other locally uncommon plants include field mouse-ear (cerastium arvense), vervain (verbena officinalis) and wild clary (salvia verbenaca).