Prior to the construction of the reservoir the site was occupied by two smaller lakes Leathes Water and Wythburn Water. The growth of the industrial city of Manchester during the 19th century had led to an increased demand for water.
The water level was raised by construction of a dam by the Manchester Corporation at the northern end of Thirlmere, in 1890–1894. The reservoir was then able to supply water to Manchester via the Thirlmere Aqueduct, roughly 100 miles long. John Frederick Bateman acted as advisor to the corporation for both projects.
There was strong local opposition to the construction of the lake and the Thirlmere Defence Association (TDA) was formed to oppose the parliamentary act which was required before work could begin. The TDA opposed it on the basis that raising the water level by 50 feet would submerge the dramatic cliffs which then surrounded the lake and a receding shoreline in summer would expose the smelly and unsightly lake bed. The organisation managed to stall the reading of the act in parliament in 1878 but the act was passed at the second reading in 1879.
Coordinates 54°32′N 3°04′W