Etang de la Gruère
The Etang de la Gruère is a dammed-up bog lake, which is located in a depression on the high plateau of the free mountain in the Swiss canton of Jura. It is located at 998 m above sea level. M. on the communal land of Saignelégier, about halfway between Saignelégier and Tramelan. The lake is 600 m long, a minimum of 60 m wide and about 4.5 m deep. The nature reserve Etang de la Gruère comprises northeast with the forest area around the actual lake and two other small bog ponds of which an area of about 1 km ².
The high moor, the Etang de la Gruère located on the porous limestone bedrock of the mountains free. By glacial erosion during the ice ages and fluvial erosion surrounding hilltops and ridges were eroded over time and troughs lined with marl and clay, which abdichteten the permeable surface. On these impermeable layers a raised bog developed in the Holocene. Today, the peat layer within the Etang de la Gruère is about 6 to 8 m thick. The lowest peat layers possess an age of 12,000 to 15,000 years. Based on the flower dust, which is preserved in the peat, the climate and forest history of the region can be reconstructed.
In this high moor that earlier contained a pond, 17th century, the Etang de la Gruère was dammed by an earth dam in the 50s. He was supposed to serve as a reservoir for the operation of a mill, so that sufficient water power was also present in periods of low rainfall. Later became a sawmill on the site of the mill. The seawater shows the typical moorland brown color with fine Torfresten and humic substances. The effluent from the Etang de la Gruère water is only around 200 m at the surface, then it disappears into a deep sinkhole and only occurs in the basin of Tramelan light again.
The high marsh zone has a unique vegetation with peat moss, moss and moor berry, blueberry bushes and rosemary. The adjacent forests consist mainly of spruce, stone pine and bog birch and dwarf birch. In 1963, the area, the Etang de la Gruère was put under protection. Today, a trail leads around the heath.