Type: Karst spring
It is the second richest karst spring in Germany. This is where the river Blau rises, which flows into the Danube after around 22km (13.7 mi). The water from the spring has carved out a large cave system over the years. Numerous legends were formed over the centuries, which should explain the blue color of the water. Physics could refute the legends and provide clarity. Today we know that tiny lime particles are floating in the water, which scatter the light (Rayleigh scattering), which leads to the deep blue color of the water. This makes the Blautopf so unique and an absolute eye-catcher for visitors.