Ruislip Lido ( RY-slip LY-doh) is a reservoir and artificial beach in Ruislip, within the London Borough of Hillingdon, England, situated between Ruislip Common, Ruislip Woods (a Site of Special Scientific Interest), and Poors Field.Originally opened as a feeder reservoir for the Grand Junction Canal in 1811, the reservoir was reopened in 1933 as a lido, with facilities for swimming and boating.