Warley Moor Reservoir, also known as Fly Flatts Reservoir, is a drinking water reservoir in West Yorkshire, England, owned and operated by Yorkshire Water.

[1] Completed in 1872, the reservoir was built by the engineer John Frederick La Trobe Bateman.

[2] The first sod was cut on 20 May 1864, by the then Mayor of Halifax, William Holdsworth, who used a silver spade with the inscription:[2] Halifax Corporation – The first sod of the Warley Moor Reservoir was turned with this spade, on Friday, the 20th May, 1864, by William Irving Holdsworth, Esq., Mayor of Halifax; J. F. Bateman, Engineer; John Parkinson and Joseph Mann, contractors; J. E. Norris, Town ClerkThe reservoir covers 68 acres (28 ha), is 45 feet (14 m) deep when full and holds up to 193,000,000 imperial gallons (880,000,000 L).

[2] It was notably described in Whiteley Turner's 1913 book A Spring-Time Saunter: Round and About Bronte Land.

It is also famous for being the reservoir Tommy Lee Royce cycled to in Series 3 of the BBC show Happy Valley.