Gosausee lies at the head of the Gosau valley in the Salzkammergut of Upper Austria, with the Hoher Dachstein and its glaciers shutting the far end and the limestone teeth of the Gosaukamm closing one side. The flat path you walk around it was blasted out of the rock. Before the power station that shore could not be walked at all: the cliffs dropped straight into the water, and the way to the high pastures ran along the other bank. In 1907 the first works on the Gosau power chain cut a construction road through the rock of the Lärchkogel, along the left shore and on up to the back lake. The dam builders' road is now the family stroll, an hour of level ground under the walls. The lake behind it is a reservoir. Every winter, when electricity is worth most, the turbines draw it from seventy-five metres deep down to thirty-six, which leaves you grey gravel flats where the shoreline should be.
It refills on Dachstein snowmelt through May and June. A lean spring leaves those flats showing into early summer. Held at its full level the water reaches its deepest green and its greatest clarity, which is what brings divers. From about mid-October the larches above both lakes turn yellow and orange against the dark spruce. The Gosaukammbahn lifts you off the shore to the Gablonzer hut on the ridge in a few minutes. The routes along the Gosaukamm begin there, and the Dachstein stands opposite you at eye level, glaciers and all. On foot, a path past the far shore takes you through alpine pasture for an hour and a half. Then the valley pinches shut and the Hinterer Gosausee appears under the rock, with the Great Gosau Glacier hanging over it. That back lake is the reason this valley has three power stations instead of five. When the operators ran dye tests they found its basin is not watertight: the water disappears into the limestone and comes out again far away, near Hallstatt.