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Lake Biel or Lake Bienne ( ; ) is a lake in western Switzerland. Together with Lake Morat and Lake Neuchâtel, it is one of the three large lakes in the Jura region of Switzerland. It lies on the language boundary between German and French speaking areas.
Geography
The lake is 15 km long and up to 4.1 km wide. Its surface area is 39.3 km<sup>2</sup>, the maximum depth 74 m. The lake is located at 429 metres above sea level.
Lake Biel/Bienne has a catchment area of about 8,305 km<sup>2</sup>. Water remains in the lake for an average of 58 days. The rivers Aare and Zihl/Thielle flowing from Lake Neuchâtel, the Twannbach draining water down from the surplombing first Jura mountain range and the Suze draining water down from the Vallon de St. Imier, are the main tributaries. The Aare was redirected into the lake in 1878, in order to prevent the flooding of the nearby area called "Seeland", and drains the water out of the lake down to Büren through a simultaneously man-made channel. The level of all three lakes is being controlled by a dam built across the channel, in Port.
The lake contains the Île de St Pierre, where Rousseau resided for a short time in 1765.