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The Obersee ("upper lake") is the smaller of the two parts of ''Zürichsee'' (Lake Zürich) in the cantons of St. Gallen and Schwyz in Switzerland. == Geography == ] ''Zürichsee'' is the common name for the ''lower'' (''Untersee'') northwestern section of , while the smaller southeastern ''upper'' (''Obersee'') lake area measures , separated by the Seedamm causeway, a Molasse formation connecting Rapperswil with the Hurden peninsula. To 1951 the annual water level fluctuations amounted more than , since then the water level is strictly regulated and therefore between summer and winter in the average differs at . The average lake level is now at 406 metres above sea level, while ''Obersee'' and ''Untersee'' differ by only .〔 The ''Seedamm'' between Rapperswil and Hurden was used since about 5,000 years as a historical lake crossing. Since the 1870s a partially artificial road causeway and two bridges were added, to cross the most narrow and flatbedded area of the lake, carrying a railway line and road from Rapperswil to Pfäffikon. Seedamm divides the southeastern section of lower ''Zürichsee'' and ''Obersee'', connected by the Hurden canal at Hurden, where also the ''Frauenwinkel'' protected area is situated. That bigger part of the ''Zürichsee'' to the west of the Seedamm, is largely situated in the canton of Zürich, smaller parts in the cantons of Schwyz and St. Gallen (Kempraten and Rapperswil), whilst the upper lake is shared just between the cantons of St. Gallen and Schwyz. Zürichsee was formed by the Linth river, which rises in the glaciers of the Glarus Alps. On occasion of the Linth river correction it was diverted by the Escher canal (completed in 1811) into Walensee (Lake Walen) from where its waters are carried to the east end of Obersee by the Linth canal (completed in 1816), and separated by the Buechberg hill. No further streams of importance flow into the Obersee besides the Linth and the much smaller Jona river. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Obersee (Zürichsee)」の詳細全文を読む スポンサード リンク
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