Lac de Bonlieu, in the Jura mountains. A lake that has remained wild, its marshy surroundings are home to rare plant species in Franche-Comté, characteristic of Jura mountain bogs and marshes: alkaline low marshes, high marshes and para-peat meadows. The vegetation is organized in concentric zones around the lake, depending on depth. From the shore to open water, these formations are home to common reeds, coopers' rushes, water lilies, pondweeds and charas (algae), whose colonies extend to a depth of 7 m. France