Aachtopf: Germany’s biggest Spring

The Aachtopf is Germany's biggest natural spring, producing an average of 8,500 liters per second. Production varies seasonally and in response to the weather, but the spring never runs dry. The Aachtopf is a karst spring which is located south of the western end of the Swabian Jura, near the town Aach. The name Aachtopf is compounded from Aach (meaning water in Old High German), the name of the river created by the spring. Topf can be translated as bowl and is commonly used for round, bowl-shaped springs. The Aach flows southward into Lake Constance, which empties into the Rhine.

The spring marks the southern end of a cave system which transports water from the western end of the Swabian Jura. Most of the water is derived from the Danube River and is obtained where the latter river disappears underground at the Danube Sink near Immendingen and Fridingen. Strangely, the Danube flows eastwards into the Black Sea, whereas the Rhine flows northwards to the North Sea. Therefore the water of the Aach flows under the European continental divide. This is a relatively common feature of karst stream captures.

The karst spring is connected to a huge cave, which runs northwards. The first exploration was made by Jochen Hasenmayer, a famous German cave diver. He mapped almost 1,000 feet (300 meters) of the cave between 1962 and 1969.

Harald Schetter, another German cave diver, followed in the 1980’s and explored the system to a penetration of approximately 1,960 feet (600 meters.) During the exploration, he did encounter a maximum depth of 121 feet (37 meters.) After 330 feet (100 meters), divers need to negotiate a large gas filled dome.

Unfortunately, a collapse blocks the cave after a few hundred meters. The cave may continue for several kilometers beyond the other side of the blockage. A local caving club was formed to find this "lost cave segment" by digging a shaft behind the collapse. At present, a continuation of the cave has not been found.

The cave starts at a depth of 39 feet (12 meters), and the first and divers have to negotiate a very strong outflow. After that, the cave opens up and many side-tunnels, called “The Labyrinth,” can be explored. One area features rich decorations with calcite crystals, others tunnels showcase stalagmites and stalactites, proofing that the system was a dry-cave at one point in time.

The visibility in the cave is always bad and around 6 to 7 feet (2 meters.) Some cave divers speculate the Aachtopf system could be as long as 31 miles (50 kilometers.)

The cave entry can be found here: 47°50′48″N 8°51′29″E / 47.84667°N 8.85806°E.