 The Cruachan Reservoir is 396 metres ( 1 @,@ 299 ft ) above Loch Awe , and is contained by a dam 316 metres ( 1 @,@ 037 ft ) long . The reservoir has a catchment area of 23 square kilometres ( 8 @.@ 9 sq mi ) , and is capable of holding 7 gigawatt @-@ hours ( 25 TJ ) of energy . Environmental restrictions meant that the dam had to have a " clean " structure , so the operational equipment is located within the dam wall itself . 
