Wikipedia:WikiProject Germany/Portal:Baden-Württemberg/Selected article/7

The Blautopf (German for Blue Pot; "blau" means blue, "topf" means pot) is a spring that serves as the source of the river Blau in the karst landscape on the Swabian Jura's southern edge, in Southern Germany. It is located in the city of Blaubeuren, approximately 16 km west of Ulm. It forms the drain for the Blau cave system and feeds the river Blau, which after 14.5 km, flows into the river Danube in the city of Ulm. Because of its high water pressure, the spring has developed a funnel-like shape, which at its deepest point has a depth of 21 metres (69 ft). The water's peculiarly blue color, varying in intensity due to weather and flow, is the result of chemical properties of limestone densely distributed in the water.

Numerous legends and folk tales refer to the Blautopf. Its characteristic colour was explained by the account that every day someone would pour a vat of ink into the Blautopf. Another myth stated that every time someone tried to measure the Blautopf's depth with a leaden sounding line, a water nix stole the sounding line. Therefore, it was not possible to determine the depth of the Blautopf. Because of this tale, there is a rock called Klötzle Blei ("little block of lead" in the local dialect) in the vicinity of the Blautopf.