The reservoir, also called Lake Margaret, with an elevation of , lies east of Mount Cyril, that has an elevation of , and south of Mount Geikie, that has an elevation of , both in the West Coast Range. Mount Sedgwick is to the south. The Bastion, at , which is a steep cliff face that is immediately west of Lake Magdala and north of Mount Geikie, together with Farquhar Lookout, with an elevation of , define a rough line of the northern part of the catchment area.