The Lac d'Ilay (or Lac de la Motte) is a lake in the Jura department of France. It has a surface area of 0.72 km² (180 acres). It is located in the communes of Le Frasnois and La Chaux-du-Dombief.

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  A view of the Lac d'Ilay
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  Ilay in the winter
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  The Lac d'Ilay with Grand Maclu in the foreground