Water that emerges
As the ground in a Karst area has many hollow spaces and an underground river system, all the water flowing in it must emerge somewhere.
N 51°35.398', E 10°18.618'
At the Ruhme spring the Karst layer hits a sandstone layer that cannot carry as much water and thus the water is forced to emerge from the grounds again. Pictures and an illustration are on the German web page Ruhmequelle. There is also a map of the area.
The Ruhme is the major spring of the Harz Karst Landscape and produces about 2.5 cubic meter of water PER SECOND. That is considerably more than 200 thousand liters (or 50 thousand gallons) per day.
As the water emerges from far below ground its temperature is widely independent from current weather conditions and remains between 8 and 9 degrees Centigrade all year (46 to 48 Fahrenheit).
N 51°34.610', E 10°34.450'
These little lakes changed their appearance considerably during the last decades due to the mining of gypsum. Surveys have shown that the above the surface creeks feeding the lakes bring less water than is leaving the lake, so there must be additional underground springs or creeks flowing into the lakes. Pictures and illustration are on the German web page Kranichteiche. There is also a map of the area.
A little cave nearby is dry today, but was created when the water was still higher and flushed out dissolvable layers of rock.