The Geisel is a tributary of the Saale in Saxony-Anhalt and gives its name to the Geiseltal and the Geiseltalsee.
The hostage rises in Sankt Micheln, a district of the city of Müchel. The Geiselquelle is referred to as the raid spring and was once one of the largest springs in Central Germany. It arises from the overflow water of an underground groundwater basin, which lies under the shell limestone heights of St. Micheln. The source is at a geographical altitude of 145 m above sea level. NN. The course of the river is almost 24 km long and flows into the Gotthardteich in Merseburg, whose outlet, the Klia, flows into the Saale north of the cathedral provost. The geographic altitude here is 86 m above sea level. NN.
The original Geiselmündung in the Saale was south of today's Neumarktbrücke, approximately in the Oelgrube ('Aalgrube') area. With the settlement of the valley between Domberg and Sixti Hügel, the Geisel, which ran through swampy terrain, was canalized and piped in the 19th century. This old drain can still be seen on the south-east corner of the Gotthard pond. Numerous water mills were operated along the Geisel, which was rich in fish. Its course was laid for the first time in 1540 in order to ensure smooth operation of the mills through the gradation. Because of the progressing lignite mining in opencast mines, which led to the formation of the Geiseltalsee, the Geisellauf was rerouted four more times from 1938 to 1965 at the exit from the city of Müchel. There are no more mills today; the hostage carried little water in 2011. Fish live below the spring only as far as St. Ulrich in the water.