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Aach Spring

Useful Information

Image: the "entrance" to the Aach spring.
Location: A81 exit Engen, B31 to Aach, in the village.
Open: no restrictions.
Fee: free.
Classification: ExplainKarst Spring Upper Jurassic (Malm) limestones.
Light: n/a
Dimension: see table below
Guided tours:  
As far as we know this information was accurate when it was published (see years in brackets), but may have changed since then.
Please check rates and details directly with the companies in question if you need more recent info.

path of the water from the Danube sink
length 11.7 km
downward slope 1.5 %
velocity 195 m/h
average 8,590 l/s
max 24,100 l/s
min 1,310 l/s
length 400 m
depth (below water level of the spring) 18 m
altitude 481 m asl
catchment area 240 km²
amount of limestone in the water 3,000 m³


Image: the spring itself. Below the bridge the cave starts.
1705 a loss of water between Immendingen and Möhringen is first mentioned.
1719 first hypothesis about an connection between Aach spring and Danube sink.
1886 ein Helmtaucher erkundet den Eingangsbereich des Aachtopfes.
1962 Jochen Hasenmayer dives 300 m into the Aach spring cave.
1963 mortal accident of an diver in the Aach spring cave.
1969 Jochen Hasenmayer dives 400 m into the Aach spring cave.
1979 mortal accident of an diver in the Aach spring cave.
mid 80s Harald Schetter revives exploration of the cave.


The Aachtopf (Aach spring) is the resurgence of the KarstDonauversickerung. This was proved by a dyeing experiment. The water is swallowed in Malm beta reappears in the Aach spring in Malm zeta. This means, the water flows from the older and lower strata into the younger and higher strata. The explanation is easy: the layers fall steeper than the karst water table.

Image: the other direction, view down the Aach river.

The time, the water needs from the Danube to the Aach spring, is rather short. During this time, the water changes its temperature only a little bit, the temperature of the spring water depends very much on the temperature of the Danube water. And of course, the water looses very little of its contents, unlike water in detritus, which is cleared by microorganisms. All this facts proof the existence of a huge cave system betweendanube and Aach spring. Its not really sure, they are big enough to allow humans to enter them, but it is very likely.

The Aach spring forms a small lake, similar to the one at the SpringBlautopf, but unlike the Blautopf, this spring is not deep with a cave at the bottom. The lake and the cave are rather shallow. The first one to explore the cave was Jochen Hasenmayer, the most famous German cave diver. He exploerd 1962 300 m of the cave, and in a second try 1969 he diver 100 m further. He found that the cave runs straight to the North.

At 130 m he discovered a big chamber, which he named Strömungsbahnhof (train station of the stream). In 1971 he discovered Explainrimstone pools and other dripstones at 17 m below water level, which proofs that this cave once was a Explainriver cave, only partially filled with water.

In the neighbourhood of the Aachtopf are 11 more little springs, most of them inside the Aach river, some at the shores of the river.