Thirlmere is a 5-mile long reservoir in the Lake District, roughly 4 miles south east of Keswick. It was created in the 1890s when the Manchester Corporation built a dam to raise the water level of 2 smaller lakes (Leathes Water and Wythburn Water). The 100-mile long Thirlmere Aqueduct carries water to the city.
It is bordered on its eastern side by Helvellyn and the A591, linking Keswick and Grasmere. The Kings Head Hotel is also here and is a popular spot for walkers and climbers.
Map showing location of Thirlmere Reservoir.