This superb natural lake of glacial origin is fed by the Lac de Narlay and flows into the River Ain via the Bief d'OEuf. It is without doubt the most beautiful and impressive of all the Jura's lakes. It has also been the focus of national archaeological interest since digs in 1904 brought to light lakeside pile dwellings at the site. The lake now has extensive sports and leisure facilities, and has become one of the major tourist attractions on the Route des Lacs.