Lake Biel

Lake Biel is one of the three lakes strung along the foot of the Jura range. It stretches fifteen kilometres, 4.1 kilometres across at its widest, covers 39.3 km² and drops to 74 metres at its deepest, with a mean depth of 28.5 metres. Its surface normally stands at 429 metres; on 16 July 2021, after exceptional rain, it rose to 430.94 metres, the highest level ever measured.

The water is only passing through. The catchment covers 8,305 km², the mean inflow reaches 244 cubic metres per second, and the theoretical residence time of a drop is only 58 days. Since 1878 and the first Jura water correction, the Aare has flowed into the lake and become its main tributary; the Thielle, the Suze and the Douanne stream make up the rest. At the outlet, the Port dam controls the discharge, with 650 cubic metres per second under normal conditions; further down the valley, at the Murgenthal gauging station, the figure must never exceed 850 cubic metres per second, to spare Aargau from flooding.

The lake takes its name from Biel, the bilingual town at its eastern tip. At the other end, near Erlach, St Peter's Island keeps the memory of Jean-Jacques Rousseau, who took refuge there while fleeing his detractors; many years later, that stay produced the fifth walk of the Reveries of the Solitary Walker. A second, smaller island is called the Bird Island.

Fifteen communes line the water, from Biel and Nidau in the east to Erlach, Ligerz and Le Landeron in the west. Two of them are exceptions to the Bernese rule: La Neuveville is the only one in the Bernese Jura, and Le Landeron the only one in the canton of Neuchâtel, which borders the lake at its western end.

Why this place is remarkable

Lake Biel is not only a landscape, it is a piece of hydraulic engineering. Since 1878 the Aare has flowed into it instead of around it, and the outflow is controlled at the Port dam: 650 cubic metres per second under normal conditions, and never more than 850 cubic metres per second further down the valley, to spare Aargau from flooding. On 16 July 2021 exceptional rain pushed the surface to 430.94 metres. On the same stretch of water, an island keeps the memory of Jean-Jacques Rousseau, who found refuge there and drew from it the fifth of his Reveries.

History and origin

The lake belongs to the line of water along the foot of the Jura, and its regime was remade by human hand. The first Jura water correction, in 1878, diverted the Aare into the lake: since then the river has been its main tributary, and the level of the water depends on a regulation approved by the Federal Council. The basin thus gathered covers 8,305 km², out of all proportion to the 39.3 km² of the lake itself.