It lies on the language boundary between German and French speaking areas.

Its surface area is 39.3 km2, the maximum depth 74 m. The lake is located at 429 metres above sea level.

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 level of all three lakes is being controlled by a dam built across the channel, in Port.

World famous watch brands have their sites and headquarters in the area, including the Swatch Group and Rolex movements manufacture.