Lac d'Ilay
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The Lac d' Ilay, also called Lac de la Motte, is a lake in the French Jura, in the Jura, around 14 km south of Champagnole in Franche -Comté. It is located at 774 m above sea level. M. on the floor of the municipalities Le Frasnois and La Chaux -du- Dombief and occupies an area of approximately 0.7 square kilometers. The lake is 1.9 km long, up to 400 m wide and has a small island (Île de la Motte ). Its maximum depth is 32 m.
The Lac d' Ilay lies in a valley on the plateau of Champagnole in the five lakes region. During high stages of the various ice ages, the pool was lined by the Jura glaciers with marl and clay layers, so that despite the karstic subsurface a lake could arise. According to the general strike of the Jura chains in this area of the Lac d' Ilay is oriented southwest-northeast direction. It is separated from the eastern Lacs de Maclu through a terrain rib. The riverside areas are flat and surrounded especially along the eastern shore of a swamp belt. To the east is the well from the wooded ridge of the Bois de Ban with the Pic de l' Aigle ( 993 m above sea level. M. ), flanked to the west by the height Le Laisenet ( 823 m above sea level. M. ).
The Lac d' Ilay is fed by a tributary of the Grand Maclu as well as by some sources in the area of Le Frasnois. Outflow is in the south, first above ground, then underground to the headwaters of Hérisson. The average residence time of lake water amounts according to calculations to around 10 to 13 months. Seawater is pumped for the treatment of drinking water for Le Frasnois and the region around the Chalain in two places. The Seezirkulation performed according to the dimictic type. In most winters, the Lac d' Ilay freezes completely because of his high position in a basin (formation of a cold air lake ).
The landscape around the Lac d' Ilay is under protection. In the wetlands around the lakes can be found for the region of rare plant communities, including the cutting Ried ( Cladium mariscus ).
On the island of La Motte St. Desiderius founded in the 6th century the priory of Saint- Vincent. The monks reclaimed the area under cultivation and thus put the foundation for the development of hamlets and villages. The priory was destroyed in the 17th century.