Lac d'Aydat, Volcanic dam lake in Aydat, France

Lac d'Aydat is the largest natural lake in Auvergne, a volcanic barrier lake held back by the 15 km lava flow of the Puy de la Vache and Puy de Lassolas, which dammed the Veyre river. Its surface covers 0.65 km² at an elevation of 837 m. The Île de Saint-Sidoine lies near the northern shore, not in the middle of the water.

Lac d'Aydat was created when the 15 km lava flow of the Cheire d'Aydat, from the Puy de la Vache and Puy de Lassolas, dammed the Veyre river; the same barrier also formed the neighbouring Lac de la Cassière. Some historians place Avitacum, the villa of the fifth-century senator and bishop Sidonius Apollinaris described in one of his letters, at this site.

The small island near the northern shore is called Saint-Sidoine, recalling Bishop Sidonius Apollinaris, who owned a Roman villa on the lake's edge. Some historians place his villa, Avitacum, at this very site, described in one of his letters.

The lake lies at 837 metres in the Puy-de-Dôme, with a 5.5 km path around its shore and 670 metres of open water between the beaches on either side. Swimming is supervised in summer from a marked beach zone, and a water sports base on the shore rents pedal boats and runs sailing and canoe-kayak courses. Parking areas, a campsite on the east bank and picnic areas are laid out around the water.

A wooden boardwalk at the mouth of the La Veyre River allows visitors to observe local wildlife and witness the wetland's natural water filtration in action. Many visitors miss this hidden corner, which reveals how the lake's ecology works beyond just swimming and sailing.