Lac des Brenets (Swiss name) or Lac de Chaillexon (French name) is a lake on the river Doubs on the border of Switzerland and France.

The depression in which the lake lies was formed by the movements of a glacier, while the lake itself was formed by a natural barrier around 12,000 years ago. At the downstream end is a waterfall known as the Saut du Doubs. A few hundred metres away, a bridge connects the French and Swiss sides of the lake.

The lake was effectively dried out completely during the European drought of 2022, causing all ship operations to cease.