Lac Bleu de Lesponne, Mountain lake in Hautes-Pyrénées, France

Lac Bleu de Lesponne is a lake in the Hautes-Pyrénées at 1,977 m, covering 51 ha with a depth of 120 m. Its deep blue colour comes from that depth. The shore is made of small stones and scattered dark rocks, and the Lac Vert lies about 500 m to the east.

The lake took shape during past ice ages when glaciers carved deep valleys into the Pyrenean landscape. This geological action created the basin that now holds the water.

The lake's original name was lac de Lhecou, from a pre-Celtic word lheco meaning "large stone" or "flat stone"; the name survives in the torrent that once drained the lake. Since the Middle Ages the lake has belonged to four communes of Dabantaygue in Lavedan, and since 1851 the Commission syndicale du Houscau has managed it as indivisible property.

Reaching the lake involves a several-hour hike from Le Chiroulet along marked mountain trails with steady elevation gain. Weather conditions at this altitude can change quickly, so proper hiking gear and wind protection are advisable.

At 120 metres, Lac Bleu de Lesponne is the deepest lake in the Pyrenees, which is why its water reads as an intense blue. Its original name was lac de Lhecou, from a pre-Celtic word for a flat or large stone, kept today by the torrent that once drained it.