Ruislip Lido started as Ruislip Reservoir. It is in Ruislip in the London Borough of Hillingdon, in the United Kingdom. It was opened on 5th December, 1811 as one of the reservoirs for the Grand Junction Canal by engineer John Rennie and constructor Hugh Mackintosh.
A suitable valley, that between Copse wood and Park wood, was selected and dammed. This flooded Park Hearn, a small village there.
Located on Ruislip Common, between Ruislip Woods (a national nature reserve) and Poors field. Referring to the map shows that the canal, now renamed the Grand Union Canal, is some distance to the west, and that a culvert was built to lead water to the canal at Hayes Bridge, a distance of some seven miles. Some of the route was under the ground, and parts have been built over. Part of the route includes a little known aqueduct which carries the canal feeder over the River Pinn near Woodville Gardens.
The Ruislip Lido Railway is a narrow gauge railway which all but encircles the reservoir.