The Frays River leaves the River Colne between the north-west of Uxbridge, Greater London and east of Denham, Buckinghamshire at Denham Weir. It passes Cowley and Yiewsley on the east bank where it is joined by the Pinn. It is also crossed by the Slough Arm of the Grand Union Canal which is carried on an aqueduct. It rejoins the River Colne at West Drayton. Little Britain is a lake between the Frays River and the River Colne.
The Frays River is believed to be a man-made diversion of waters from the River Colne to feed watermills around Uxbridge. The name is originates from John Fray who owned Cowley Hall beside the river in the fifteenth century. Other names for the river are the Uxbridge and Cowley Mill Stream, the Cowley Stream or the Colham Mill Stream. In the 17th century the river powered five mills. Drayton Mill at West Drayton was mentioned in Domesday Book and was used for flour milling, paper-making and the manufacture of millboard. It ceased operation in about 1923.
Frays River in Uxbridge and Cowley has a diversity of wetland plants, fish and waterfowl associated with good water quality and is a Site of Importance for Nature Conservation, Borough Grade I. Frays Island between the Frays and the River Colne is a Site of Metropolitan Importance for Nature Conservation managed by the London Wildlife Trust, and the river goes through two Sites of Special Scientific Interest managed by the Trust: Frays Farm Meadows and Denham Lock Wood.
- London Borough of Hillingdon - River Frays
- West Drayton: Mills, A History of the County of Middlesex: Volume 3 (1962), pp. 196. Date accessed: 26 October 2008
- "Frays River at Uxbridge Moor". Greenspace Information for Greater London. 2006. Retrieved 30 December 2012.
- London Wildlife Trust, Frays Island & Mabey's Meadow
- Peter Stansky and William Abrahams The Unknown George Orwell
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