From Dragon Eye Atlas

The Gleyre flows from Sumegaidau towards the east until it merges with the Kordera river about 20 km upstream from Volgen.

What makes the Gleyre special is that it is an artificial river. It flows out of an underground aquifier located in the Sumegaidau Mine, which was pierced accidentally when the miners dug too deep. A release tunnel was dug into a nearby valley, which now redirectes the flow of the aquifier away from the mine into the valley, where it flows on as the Gleyre river.