The dam, called Lake Margaret, was completed in 1918 and it was the first gravity dam constructed in Tasmania. It was built of concrete with conglomerate "plums". The dam wall is high and is long and the concrete-faced dam wall has a volume of. The uncontrolled spillway has a capacity of. In 1974 the dam wall was strengthened by the use of prestressed anchors and grouting of open joints. The Lake Margaret dam impounds the Yolande River, which also is the outflow from the dam. Further west the Yolande joins with the Langdon River, another West Coast Range west flowing river, to join with the Henty River west of the Zeehan Highway.
Reservoir
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. Numerous smaller lakes - some named and some not - lie above the location of the Lake Margaret. The vesting of the catchment with the current operator of the hydro electric power station, makes the two feeder parts of the catchment specific Hydro land in contrast to the surrounding landscape which is either in the Tyndall Regional Reserve or the Lake Beatrice Conservation Area. The two southern feeder Hydro reserves start from the slopes of Mount Sedgwick, the westerly from Lake Barnables, then to Lake Phillip. The eastern feeder starts at an unnamed lake to Lake Polycarp, Lake Peter, Lake Paul, Lake Apollos, and then to Lake Phillip. The northern feeder starts from Lake Monica, Lake Myra, then Lake Magdala, situated at , Lake Martha, at, and Lake Mary, at, before flowing into Lake Margaret. The larger lower altitude natural lake of the area lies to the south east side of Mount Sedgwick and is known as Lake Beatrice.
Power scheme
The initial purpose of Lake Margaret when it was constructed by the Mount Lyell Mining and Railway Company was to generate hydroelectric power for the -based Mount Lyell mine, railway, and surrounding community. While the mine has since closed, the purpose of Lake Margaret to generate power remains unchanged. Between 1918 and 1930 the Mount Lyell Mining and Railway Company commissioned seven conventional Pelton turbine generators with a capacity of at the Upper Lake Margaret Power Station. Hydro Tasmania took ownership of the power station in 1985. Water travels from Lake Margaret through a woodstavepipeline to the power station. In 1931 a minihydro plant was constructed to provide additional power. The single Turgo turbine generates. Hydro Tasmania took ownership of the power station in 1985 and decommissioned the plant in 1994. The station was reopened in 2010 following refurbishment that included a new penstock, turbine and woodstave pipeline.
