Concept
The Sihl is a Swiss river that rises near the Druesberg mountain in the canton of Schwyz, and eventually flows into the Limmat in the centre of the city of Zürich. It has a length of , including the Sihlsee reservoir, through which the river flows. Water is abstracted from the river at the Sihlsee, leading to decreased downstream water flows and a consequent reduction in water quality. The river flows through, or along the border of, the cantons of Schwyz, Zürich and Zug. The main settlements of the Sihl Valley are all in the canton of Zürich, and include the towns of Langnau am Albis and Adliswil, along with a south-western segment of the city of Zürich. Above Langnau am Albis, some from the confluence with the Limmat, there are no major settlements alongside the river, and only a few small villages. Whilst the town of Einsiedeln is situated close to the Sihlsee, it is actually in the valley of a tributary river, the Alp. The first written reference to the name dates to 1018, in the form Sylaha. The name may be of Old European or Celtic origin: *Sîla ("quiet watercourse", from a root *sîl = "to trickle, wet") > Romance Sila with the addition of the Old High German element aha "flowing water". The river rises to the north-eastern side of the Druesberg mountain, in the municipality of Unteriberg of the canton of Schwyz, and flows north to the village of Studen. Some downstream of Studen, the river enters the artificial Sihlsee reservoir at its southern end. Nearby, the Minster also flows into the Sihlsee, and was, prior to construction of the reservoir, a direct tributary of the Sihl. The Eubach, Rickentalbach and Grossbach tributary streams also flow into the Sihl via the Sihlsee. The Sihlsee is some long, and lies close to the town of Einsiedeln. It is Switzerland's largest artificial lake, and is impounded by a high dam. Electricity is generated by diverting water down a tunnel from the Sihlsee, which has a water level elevation of , through the Etzelwerk hydroelectric power station at Altendorf, into Lake Zürich, which has a water level elevation of .
