Thirlmere is situated in Cumbria, in the English Lake District. It is 3.5 miles long and 158 feet deep. It supplies over 10 percent of the North West's water. It has a dam with a height of 104 feet. This process has totally submerged Armboth and Wythburn with only one small church still visible. It is overshadowed by Helvellyn to the east.