Thirlmere Reservoir was originally two smaller lakes. In 1889 they were purchased by Manchester City Corporation Waterworks, to be made into a reservoir to supply water to Manchester. The area was dammed and became one large reservoir, at nearly 4 miles long.
In the process of building the reservoir, the settlements of Armboth and Wythburn were submerged. The only remaining building is the church at Wythburn.
The first stone for the dam was laid on the 22nd August 1890.
On 13th October 1894, the first water flowed into Manchester, having travelled 95.9 miles along the Thirlmere Aqueduct from Thirlmere Reservoir.