Lac du Vieux Émosson is a reservoir in Valais, Switzerland, in the municipality of Finhaut at an elevation of 2205 m. The lake drains into the reservoir Lac d'Émosson, 300 m below.

The larger capacity is used for the Nant de Drance pumped storage plant, for which Lac du Vieux Emosson forms the upper basin and Emosson reservoir the lower basin.

[1] The storage power plant went into operation on July 1, 2022, after 14 years of construction.

The construction of the plant cost the equivalent of 2 billion euros.

The lake forms the upper reservoir for the 900 MW Nant de Drance Hydropower Plant which began operations in 2022.