In the 20th century three reservoirs have been constructed on the moor ; these are Colliford Lake , Siblyback Lake and Crowdy reservoirs which supply water for a large part of the county 's population .
Inland waters on the moor include Dozmary Pool ( Cornwall 's only natural inland lake ) and three reservoirs , Colliford Lake , Siblyback Lake and Crowdy reservoir which supply water for a large part of the county 's population .