|Location||Germany, Switzerland, Austria|
|Catchment area||11,500 km2 (4,400 sq mi)|
|Basin countries||Germany, Switzerland, Austria|
|Max. length||63 km (39 mi)|
|Max. width||14 km (8.7 mi)|
|Surface area||536 km2 (207 sq mi)|
|Average depth||90 m (300 ft)|
|Max. depth||254 m (833 ft)|
|Water volume||1e10 cubic metres (3.5×1011 cu ft)|
|Residence time||4.3 years|
|Surface elevation||395 m (1,296 ft)|
|Frozen||1795, 1830, 1880 (partial), 1963|
|Islands||Mainau, Reichenau, Lindau|
|Sections/sub-basins||Obersee, Überlinger See; Untersee, Zeller See, Gnadensee|
Lake Constance (German: Bodensee) is a lake on the Rhine at the northern foot of the Alps, and consists of three bodies of water: the Obersee ("upper lake"), the Untersee ("lower lake"), and a connecting stretch of the Rhine, called the Seerhein.
The lake is situated in Germany, Switzerland and Austria near the Alps. Specifically, its shorelines lie in the German federal states of Bavaria and Baden-Württemberg, the Austrian federal state of Vorarlberg, and the Swiss cantons of Thurgau and St. Gallen. The Rhine flows into it from the south following the Austro-Swiss frontier.
Lake Constance was first mentioned by the Roman geographer Pomponius Mela about 43 AD. He noted that the Rhine flows through two lakes, and gave them the Latin names Lacus Venetus (Obersee) and Lacus Acronius (Untersee). Pliny the Elder used the name Lacus Brigantinus, after the Roman city of Brigantium (today Bregenz). The lake is also colloquially known as the Swabian Sea (das schwäbische Meer).
The freshwater lake sits at 395 m (1,296 ft) above sea level and is Central Europe's third largest, after Lake Balaton and Lake Geneva. It is 63 km (39 mi) long, and at its widest point, nearly 14 km (8.7 mi). It covers approximately 571 km2 (220 sq mi) of total area. The greatest depth is 252 metres (827 ft) in the middle of the eastern part (Obersee). Its volume is approximately 1e10 m3 (1.3×1010 cu yd). The lake has four parts: the main section, called Obersee, 476 km2 (184 sq mi); the north section, Überlinger See, 61 km2 (24 sq mi); the west section, Untersee, 63 km2 (24 sq mi); and the northwest section, the Zeller See and Gnadensee. The regulated Rhine flows into the lake in the southeast, through the Obersee, the city of Konstanz and the Untersee and flows out near Stein am Rhein. Lake Constance provides fresh water to many cities in south Germany.
Lake Constance was formed by the Rhine Glacier during the ice age and is a zungenbecken lake. The Rhine, the Bregenzer Ache, and the Dornbirner Ache carry sediments from the Alps to the lake, thus gradually decreasing the depth of the lake in the southeast.
The lake was frozen in the years 1077 (?), 1326 (partial), 1378 (partial), 1435, 1465 (partial), 1477 (partial), 1491 (partial?), 1517 (partial), 1571 (partial), 1573, 1600 (partial), 1684, 1695, 1709 (partial), 1795, 1830, 1880 (partial), and 1963.
Approximately 1,000 tonnes (1,100 short tons) of fish were caught by 150 professional fishermen in 2001 which was below the previous ten year average of 1,200 tonnes (1,300 short tons) per year. The Lake Constance trout (Salmo trutta) was almost extinct in the 1980s due to pollution, but thanks to protective measures has made a significant return. Lake Constance was the home of the now extinct species of trout Salvelinus profundus. as well as of the Lake Constance whitefish (Coregonus gutturosus).
The lake itself is an important drinking water source for southwestern Germany, called Bodensee-Wasserversorgung ("Lake Constance Water Supply").
After the Council of Constance, the Catholic world gave the lake its current name, after the city Constantia (Konstanz), that, in turn, was named after a Roman emperor (either Constantius Chlorus or his grandson Constantius II). The German name, Bodensee, derives on the other hand from the place name Bodman (today's Bodman-Ludwigshafen) just north of Konstanz.
International borders 
The Lake Constance is the only area in Europe where are no boundaries exist, because there is no legally binding agreement as to where the boundaries lie between Switzerland, Germany and Austria where these three countries meet in Lake Constance. While Switzerland holds the view that the border runs through the middle of the lake, Austria is of the opinion that the lake stands in condominium of all the states on its banks. Germany holds no unambiguous opinion. Legal questions pertaining to ship transport and fishing are regulated in separate treaties.
Naturally, disputes arise. One concerns a houseboat which was moored in two states (ECJ c. 224/97 Erich Ciola); another concerns the rights to fish in the Bay of Bregenz. In relation to the latter, an Austrian family was of the opinion that it alone had the right to fish in broad portions of the bay. However, this was accepted neither by the Austrian courts nor by the organs and courts of the other states.
Recent floods 
- A 100-year flood around June 1999 (Pfingsthochwasser 1999) raised the level about 2 metres above normal, flooding harbors and many shoreline buildings and hotels.
- In late August 2005, heavy rains raised the level by more than 70 cm in a few days. The rains caused widespread flooding and washed out highways and railroads.
Islands in the lake 
The three major islands are:
This is a complete list of the islands in Lake Constance, listed from east to west:
|1||Galgeninsel||peninsula since 19th century||-||Lindau (Reutin district)||
|2||Hoy||53||-||Lindau (Reutin district)||
|3||Lindau||680,000||3,000||Lindau (Island district)||
|4||Wasserburg||peninsula since 1720||27||Wasserburg (Island district)||
|5||Mainau||447,584||185||Konstanz (Litzelstetten district)||
|6||Dominikanerinsel||18,318||21||Konstanz (Altstadt district)||
|7||Mittlerer Langbohl||31,254||-||Konstanz (Industriegebiet district)||
|8||Triboldingerbohl||135,570||-||Konstanz (Industriegebiet district)||
|10||Liebesinsel||300||-||Radolfzell (Mettnau district)||
|11||Werd||15,854||9||Eschenz (Untereschenz district)||
|12||Mittleres Werdli||4,000||-||Stein am Rhein||
|13||Unteres Werdli||6,000||-||Stein am Rhein||
|Lake Constance Islands||5,637,079||6,400||6 municipalities|
Towns and cities at the lake 
From the entry of the Rhine, on the northern or right shore:
- On the Upper Lake (Obersee) and Überlinger See
- Konstanz with suburbs
- On the lower lake (Untersee)
From the entry of the Rhine, on the southern or left shore:
- On the Upper Lake (Obersee)
- On the Rhine
- On the Lower Lake (Untersee)
See also 
- 2002 Überlingen Mid-Air Collision
- Württembergischer Yacht Club
- Lake Constance is also the title of a track from Mike Oldfield's The Millennium Bell album
- Gordon McLachlan. The Rough Guide to Germany. Rough Guides Ltd. London, 2004. ISBN 1-84353-293-X.
- Image #432, Flying Camera Satellite Images 1999, Lloyd Reeds Map Collection, McMaster University Library.
- IUCN Red list
- Red List - Volume 1: Vertebrates (2009) - General assessment for the vertebrate groups
- "Bodensee-Wasserversorgung", German language Wikipedia.
- David Mark and Barry Smith, et al., Bizarre Shapes: 100 Geographic Monsters.
- Rolf Zimmermann: A look at Lake Constance. Stadler Verlagsgesellschaft mbH. Konstanz 2004. ISBN 3-7977-0507-7. (Pictures and texts of the cities around Lake Constance).
|Wikimedia Commons has media related to: Lake Constance|
- Bodensee-Hochwasser (German) waterlevels
- Internationale Bodenseekonferenz
- Regio Bodensee Statistics
- Lake Constance: pictures
- Photos of Lake Constance
- Bibliography on Water Resources and International Law Peace Palace Library
- GrenzRaumSee: A project from the Ludwig-Uhland-Institut für Empirische Kulturwissenschaft (Ludwig-Uhland-Department of European Ethnology / Empirical Cultural Science) of the University of Tübingen
- Lake Constance/Bodensee Lessons learned managing the lake
- Lake Constance Accommodation
- Tourist Information Lake Constance
- Karl Heinz Burmeister: Lake Constance in German, French and Italian in the online Historical Dictionary of Switzerland.
- Nixdorf, B.; et al. (2004), "Bodensee", Dokumentation von Zustand und Entwicklung der wichtigsten Seen Deutschlands (in German), Berlin: Umweltbundesamt, p. 4